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->''He replied, "If you have faith as small as a mustard seed, you can say to this mulberry tree, 'Be uprooted and planted in the sea,' and it will obey you."''
-->-- '''{{Jesus}}''' addressing his disciples, ''Literature/TheBible'': Luke 17:5-6

An old trope, wherein enough belief in something will actually cause things to happen, also known as "magical thinking". This isn't a MagicFeather where "confidence" merely allows one to use their own abilities to the fullest; this actually physically changes the universe. In particular, a somewhat [[PostModernism post-modern take]] on divine pantheons posits that [[GodsNeedPrayerBadly gods are the product of (or severely dependent upon) their believers.]] Take away their believers, and a god "fades away."

This creates a vicious cycle for non-believers, as magical events are "[[PuffOfLogic disproven]]" in their presence because they don't believe in the first place, thus cementing their disbelief. Particular savvy characters may [[JustIgnoreIt take advantage of this]] by getting others to yell "ImNotAfraidOfYou!"

A variant of this trope crosses it with IAmSpartacus, with the hero asking the people watching the battle to lend their belief/hope/faith in order to help. A further variant, common in works aimed at children (and their parodies) involves one character [[BreakingTheFourthWall turning to the audience and asking them]] to clap their hands/stomp their feet/whatever to accomplish whatever needs to be accomplished at the time.

The lead quote is from Literature/TheBible, making this OlderThanFeudalism.

Not to be confused with YourMindMakesItReal, which has more to do with characters getting physically hurt with The Power Of Imagination (though the two tropes do sometimes intertwine). For those who don't even ''need'' to clap, see RealityWarper. Compare with WillingSuspensionOfDisbelief. See also AllMythsAreTrue, PsychoactivePowers, PuffOfLogic, & TheTreacheryOfImages. Has nothing to do with ClaspYourHandsIfYouDeceive.

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!!Examples:

[[foldercontrol]]

[[folder:Anime and Manga]]
* ''Webcomic/AxisPowersHetalia'': Mystical ancient Shinto creatures and ghosts are disappearing and leaving Japan because not just the people of Japan but also Japan himself don't believe in them anymore. There's always England...
** Speaking of England, a common theory about his "{{Imaginary Friend}}s" is that they're all actual, real fractions of European folklore and that the reason England can see them is because he's the only one who still believes in them.
** A popular {{Fanon}} theory has it that nations are [[AnthropomorphicPersonification manifestations]] of their respective countries' people, culture and national identity, not any political entities. They die when their culture fades away and no one identifies with them anymore.
* ''Manga/{{Berserk}}'': Answering the wider question as to why the world of Berserk is so full of [[CrapsackWorld crapsuck]], [[spoiler: humanity needed a reason as to why there was so much evil and suffering in the world so badly that all of their collective thoughts and prayers formed the [[GodIsEvil Idea of Evil]]. Yep. That will do it.]]
* In ''Manga/{{Bleach}}'', the MaskedLuchador Mask De Masculine gets stronger and heals from all damage the more people cheer for him. While he is incredibly powerful even without his fans, [[ShootTheMedicFirst his fans have to be taken out first]] before he can be killed.
* ''LightNovel/ACertainMagicalIndex'': [[spoiler:Aureolus Izzard]]'s incredible [[RealityWarper powers]] are limited by what he thinks his limits are; if he loses confidence in his power and stops believing in its effectiveness, reality obliges.
** All espers derive their powers from having radically different internal realities from the standard. The process involves little kids, experimental drugs and brainwashing. Lots of parents seem to have no problems volunteering their kids for the process. Since the process is repeatable, it's Scientific, as opposed to the methods of the magicians... Waitaminute!
* The part where the trope crosses over with IAmSpartacus is the principle behind Goku's Genki-dama/Spirit Bomb in ''Manga/DragonBall'': he draws energy from the Earth, including its people, to power it up. Addressed straight in [[spoiler:his final battle with Buu, when Mr. Satan/Hercule asks the (remaining) people on Earth to lend their energies to him for this specific purpose.]]
* The world of Gaia in ''{{Escaflowne}}'' was actually built to some extent around the trope, as it was believed to have formed from the will of the ancient people of Atlantis. More concretely, [[spoiler:Hitomi's sense of belief is so strong that she starts reshaping events around her, even to the extent of trumping the already-daunting ability of Zeibach to invoke WindsOfDestinyChange.]]
* In ''FateKaleidLinerPrismaIllya'', the main character Illya, can fly because she was a fan of [[MagicalGirl Magical Girls]] before becoming one and believes that all Magical Girls have to be able to fly. Miyu on the other hand, can't fly because she is smart and can't ignore the laws of physics.
* ''Lightnovel/FullMetalPanic'': the Lambda Driver reacts to the user's mental state. The first time Sousuke uses it, Kaname instructs him that he must believe in it for it to work.
* In the manga, ''HydeAndCloser'', [[ABoyAndHisX Shunpei and his animated]] [[ChainsawGood magical chainsaw-wielding bear toy]] must fight off magicians out to kill him, all while learning magic in order to defend himself. Hyde explains that the source of all magical power is belief; the point of the strange rituals is to convince the spellcaster of the spell's reality.
* In ''{{Kanon}}'', [[spoiler:the comatose Ayu still believed enough in her promise to Yuuichi and the wishes that she made on a simple crane machine doll that she was able to spiritually project herself as a solid living being even seven years later.]]
* In "The Land of the Will, Cephiro" in ''Manga/MagicKnightRayearth'', the "heart that believes" shapes the world around them.
* In ''Manga/MahouSenseiNegima'', apparently you only have a soul if you believe you have one. [[spoiler: When Negi makes out with Chachamaru to initiate a Pactio (which requires that she has a soul to get one), despite Chachamaru all but giving up, Negi believes in her so much that she gets both a soul and a Pactio.]]
* The ''MermaidMelodyPichiPichiPitch'' manga has the Purple Harp, which loses its strings when Lucia fears that she'll fail, and regains them when Hanon and Rina tell her to believe in herself.
* In the {{Nasuverse}}, the Gods of old were willed into existence ''because'' people believed they exist. This also explains their downfall, as the number of believers declined... or because their believers think they all died in some massive slugfest (like Ragnarök). Other examples from Nasu include the summoned spirits of dead heroes, who become stronger if their legend is better known, and a weapon designed by the Catholic church for defeating a reincarnating vampire by shoving their belief that reincarnation doesn't exist forcibly down his throat. Or through his liver. Whatever works.
** Even "reality" itself is an illusion conjured by "Gaia". A Reality Marble manifests when a person with a radically different internal reality (i.e. someone with a ''very'' distorted sense of self) believes in his/her own reality so strongly that it ''temporarily overpowers the will of the Earth''.
* A [[EldritchAbomination not-so-nice]] version is a major plot point in ''Anime/ParanoiaAgent''. [[spoiler:Belief in the UrbanLegend of Shonen Bat led to him becoming real]], and unpleasant, freaky, and ''[[GainaxEnding completely incomprehensible]]'' things ensued.
* ''Anime/{{Pokemon 3}}'' crossed this trope with [[RealityWarper Reality Warping]], resulting in the Unown being driven crazy by their own creation, and then being stopped by Entei when Molly Hale began believing in him.
* In ''LightNovel/{{Slayers}}'', Shinzoku are dependent on the prayers of the mortal races, to the point where their counterparts, Mazoku, tactically destroyed temples to reduce the power of Shinzoku. Mazoku have their own form, feeding off of any negative emotions the mortal races have.
** In the Novels, Lina was once confronted by Dynast Graushera's General, a very powerful Mazoku. Realizing she couldn't fight or escape, Lina decided to try mocking said Mazoku's name. The reasoning was that because Mazoku were masses of astral energy held together by their own self image, anything that undermined their self confidence would make them weaker. The strategy works.
* Spiral power in ''Anime/TengenToppaGurrenLagann'' is given several different TechnoBabble explanations, but the effective result is that if you truly believe you can win, you ''will'' win. (Possibly by virtue of a HumongousMecha the size of a ''galaxy'' forming itself out of pure willpower.) Conversely, pilots afflicted with [[HeroicBSOD sudden pangs of doubt]] are apt to find their robots powering down, which is [[DangerouslyGenreSavvy ruthlessly exploited]] by the Anti-Spirals, using tactics designed to induce fear and despair to try and shake that confidence.
** It's also established that, due to Spiral Power, a Gunman's controls are set to how the pilot thinks it should be controlled. It's possible for someone with no prior training to get into a Gunman, move some joysticks, and get it working solely because that's what they want it to do.
* In ''VisualNovel/UminekoNoNakuKoroNi'', the point of Battler's game with the witch Beatrice is that, should he accept her existence and the existence of magic, magic will exist in retrospect as the cause of the murders that drive the whole mystery. Since he refuses to accept her existence, though, Beatrice must prove her existence with [[LockedRoomMystery new unsolvable murders.]]
** This is also poor [[spoiler:Hanyuu]]'s dilemma in ''VisualNovel/HigurashiNoNakuKoroNi'', as lack of faith by the residents is the cause of [[spoiler:her]] weakened powers.
* In ''Anime/WelcomeToTheNHK'', a large number of the episodes are spent with the protagonist Tatsuhiro Sato having hallucinations of characters, scenarios, and people are members of an organization out to ruin his life. Near the end of the series, he asks one of the other cast members to see one of these creatures, where it is revealed to her. [[spoiler:He then imagines his cell phone is a bomb and jumps off a cliff to blow up with it in a suicide attempt.]]
[[/folder]]

[[folder:Comic Books]]
* In ''Crimson'', it's apparently the vampire's religious background that counts, as one man learns when the vampire he's trying to ward off takes his cross away and beats him with it, remarking "My name is Steinman, [[YiddishAsASecondLanguage schmuck]]! Why would this work on me?"
* The Creator/DCComics character ''Dr. Thirteen'' was a skeptic who disproved hauntings. Since he was established as existing in Franchise/TheDCU, and eventually encountered ComicBook/ThePhantomStranger, the fact he was always right in his ''own'' stories seemed strange and turned him into a FlatEarthAtheist, until Creator/NeilGaiman's ''ComicBook/TheBooksOfMagic'' explained that his complete dismissal of magic meant he lived in a personal world where there was none.
* ComicBook/{{Excalibur}} member Meggan was an [[EmpathicShapeshifter empathic adaptive shapeshifter]] -- she looked like what people expected her to look like, and consequently spent a good part of her childhood turning into a monster. Eventually, she managed to develop a strong enough sense of identity that other people's expectations no longer affected her shapeshifting.
** In one of those cosmic ironies, the current powerset of CaptainBritain, Meggan's husband, depends on his own confidence, much like Gladiator below - the stronger his confidence, the stronger he becomes.
* The living myths in ''Comicbook/{{Fables}}'' are made stronger by those who believe in them. This is used to explain why some lesser-known fables are killed, but Snow White can take a rifle shot to the head and survive, albeit with long-term consequences.
** This is turned into a plot point later, when Jack Horner (of "Jack and the Beanstalk," "Jack The Giant Killer," and several other stories) decides to increase his personal power by releasing a series of Hollywood blockbusters about himself.
** Also, not ''every'' Fable gets their power from this; Frau Totenkinder specifically gets her power from 'other' sources. (Don't ask.) Popularity equals power is a theory that's never been tested under controlled conditions.
*** Subverted by [[spoiler:the death of Little Boy Blue in # 82]]. The subversion was the huge power of the character in question, as the character itself isn't neither well known nor anywhere near as popular as Snow White and her peers.
* In the August 1966 issue of ''TheFlash'', Barry Allen starts to fade away from existence once a villain unleashes a ray that causes everyone to not believe he exists. Everyone except a little orphan girl he had helped before forgets that he really exists until he and the orphan girl start a massive letter writing campaign to force people to remember The Flash.
** This issue is somewhat prescient considering that the DCU contains an actual comic book limbo where characters (often those who haven't appeared in books for quite some time in the real world) go to when people start to forget their stories.
* This is central to one of Warren Ellis' stories for ''ComicBook/{{Hellblazer}}''. An occult writer "acquires" a magical item called The Crib, and sets about killing people with it. The thing is, there's no such artifact, and it only works because both he and his victims believed in it. John Constantine, being more knowledgeable about the truth of the occult world, ''knows'' there's no such item, so it has no effect on him, and he's able to reveal what the person ''actually'' had -- an old cereal box with a dead mouse in it. It's discussed in earlier stories that magic in general works on this principle, but this is the first one where it really takes center stage and we see just how far it goes.
* Another example from the MarvelUniverse is the Shi'ar Imperial Guard commander Gladiator: His strength is based on his own belief in his power. Shake his confidence and he can be beaten easily, rev it up and he crushes stars with his fists.
** His son Kid Gladiator has the same basic powers and an even bigger ego, being a [[TeensAreMonsters teenager and all]]. Nothing, ''not even temporarily being turned into a Brood'', has managed to shake him up.
** According to ComicBook/MarvelAdventures (and possibly main 616 canon), Dr. Strange's magic works the same way. He deliberately cultivates a LargeHam persona to boost his own confidence.
* Yet another example from the Marvel Universe are the Cardinals, who serve as the elite shock troops/assassins for the Universal Church of Truth. The Church collects the Prayer Power of it's trillion-plus faithful worshipers, then converts that prayer power into energy and stores it in belief batteries. The Cardinals can tap into that immense power reserve, giving them the power to do anything if they believe they can. Hence the Cardinals can shoot energy beams, create force fields, and etc. because some convert on the other side of the galaxy believes they can do that.
** It doesn't even have somebody else, it could be the Cardinal himself who [[http://www.comicvine.com/cardinals/65-55707/all-images/108-195836/cardinals_01/105-693528/?offset=0 believes]].
* [[SubvertedTrope Subverted]] by Walt Simonson in ''Orion # 24'':
-->''You've read too much fiction, Arnicus. Gods are not dependent on their worshipers; worshipers are dependent on their '''gods.'''\\
And the '''New Gods?''' We're as old as time, constantly remade, constantly reborn with each turning of the wheel.\\
No '''worshipers? Fool!!! Look about you!''' Each time a mortal turns on a computer, puts a piece of bread in the toaster, opens a door, strikes a match, or wonders at the stars...\\
...he '''worships''' at the altar of the New Gods.''
* Gods and other supernatural beings in Creator/NeilGaiman's ComicBook/TheSandman live off of this trope which shows up in his other writings as well.
** In one issue there is a story that the world was once run by cats the size of men and humans were the size of cats and were just playthings and servants. Dream told a human that if enough of them dreamt that things were different they would be. After most of humanity dreams that they were in charge the universe is rewritten so that cats had never been the dominant life and nobody remembered these events (except for Dream who naturally tells a cat this story and that they can change it back with enough belief).
** When they turn up in a GrantMorrison issue of ''JusticeLeagueOfAmerica'', the heroes are sent into a boy's nightmare world, where a telepathic conqueror has created a world where it has already won and there are no heroes to stop it. As the boy's belief wanes, so do their powers.
* Used in MarvelComics in {{Thor}} # 301, where it was revealed that, while the gods themselves ''could'' exist long after they had no more worshipers, those who STILL have some had greater amounts of power. Also, a god is stronger in his home plane than gods from another.
* In ''Thor Meets Captain America'' by David Brin, this trope is used by the hero. His actual words are [[http://davidbrin.com/thor1.htm "I don't believe in you"]].
* When the ComicBook/{{X-Men}} faced off with Dracula, Kitty Pryde tries using a crucifix against Dracula and achieves nothing. Dracula then grabs her throat, and burns his hand on her Star of David necklace. No points for guessing Kitty's religion, folks!
** Wolverine is unable to repel Dracula with a cross, but when devout Nightcrawler takes up the symbol, Drac is driven back.
[[/folder]]

[[folder:Fanfics]]
* ''FanFic/CrownsOfTheKingdom'' has this in its ending. Everyone believes in Mickey and Minnie to restore them from nonexistence.
* The entire premise of ''Fanfic/MyLittleUnicorn'' is based around this. The author has stated in forums that he believes in this concept.
* In the ''FanFic/PonyPOVSeries'', it's eventually revealed that Discord's eldest brother [[UnPerson D____t]] was the AnthropomorphicPersonification of what is basically this concept, the ability by mortals to will things into existence. However, when he was [[RetGone erased from existence]] by Their Mother [[EldritchAbomination Entropy]], his concept disappeared with him, denying mortals this ability.
* "True magic" works this way in ''FanFic/DiariesOfAMadman'', which makes it far more powerful than unicorn magic, but much more difficult to master.
* [[TheSlenderManMythos In the Slender Man fic]] ''Fanfic/ByTheFiresLight'' the Slender Man would not exist if people did not believe in him.
[[/folder]]

[[folder:Films -- Animated]]
* ''WesternAnimation/CareBearsMovieIIANewGeneration'', in which the audience is encouraged to say "I care!" to save a dying little girl, which not only succeeds, but acts as LoveRedeems for the BigBad.
* Inverted in ''WesternAnimation/TheFlightOfDragons'' where the protagonist Peter defeats the evil wizard Omadon by 'denying' that he exists, and since magic relies on human belief to exist Omadon crumbles away to nothing. A list of hard, proven sciences to counter Omadon's list of magic creatures hurts too, fighting dark dreams with the proven and repeatable.
* In ''WesternAnimation/YogiBear and the Magical Flight of the Spruce Goose'' Yogi gets his friends out of the cargo hold of the eponymous airplane by having them ''believe'' a set of doors into existence.
-->'''Booboo:''' This is the part where he goes Tinkerbell on us.
[[/folder]]

[[folder:Films -- Live-Action]]
* In ''Film/ACountryChristmas'' Santa's powers, and then his very existence, depends on people believing on him.
* In ''Film/{{Candyman}}'', the eponymous character was actually created by the people's belief. Interestingly enough, after [[spoiler:Candyman dies in the climax of the film, the people's belief shifts to Helen: as a result, she becomes a murderous spirit like Candyman.]] The sequels, though, are a different story.
* Parodied again in ''Film/{{Dracula 2000}}''. One of Team Good Guy brandishes a crucifix at one of the vamps, who remarks "Sorry, sport. I'm an Atheist." The good guy wittily remarks "God loves you anyway." before stabbing the vamp in the eye with the knife hidden inside the crucifix.
* In ''{{Film/Elf}}'', Santa's sleigh won't fly without the proper amount of Christmas spirit from people believing in him. Or engines, which he's used since the 70s to keep his sleigh aloft as Christmas spirit has gone down.
* In ''Film/ErikTheViking'', Harald the Missionary who accompanies the Vikings on their quest staunchly refuses to believe in Ragnarok and any of the Viking myths. Eventually, the Vikings make their way to Valhalla, where they triumphantly demand that the missionary accept that they were right all along - only to discover that because he doesn't believe in it, he can't actually see it, and causing a certain amount of frustration. This actually saves them in the end, as because Harald doesn't believe in the Aesir they have no power over him. He can walk through the walls of Valhalla, make it back to the ship, and use the MacGuffin to bring them all back home while the other Vikings are trapped.
* In ''Film/TheFearlessVampireKillers (or Pardon Me But Your Teeth are in My Neck)'', a cross fails to work on a Jewish vampire. In the mock documentary at the end of the film, an expert on vampires notes that the effectiveness of the religious symbol depends not on the human wielding it, but the vampire itself. Crosses work on Christians, Stars of Davids work on Jews - but the expert warns that using a Star of David on an Arab vampire will only make it angry.
* A woman in ''Film/{{Feast}} II: Sloppy Seconds'' tries to believe her way out of terrible situation after terrible situation.
* In ''Film/FreddyVsJason'', Freddy Krueger's weakness is that he only has power so long as people ''believe'' in him, so he has to bring Jason back to remind them. This hearkens back to the original ending for ''Film/ANightmareOnElmStreet1984'', where he's defeated by Nancy refusing to believe in and fear him any longer, robbing him of his powers - in the theatrical release, this only ''appears'' to work.
* ''Film/FrightNight''.
-->'''Peter Vincent:''' ''[brandishing a crucifix]'' Back, spawn of Satan!\\
'''Jerry Dandrige:''' ''[chuckles]'' Oh, really? ''[[[NoSell grabs the cross, crushes it, and throws it aside]]]'' You have to have faith for this to work on me.
** Later they face off again, and Jerry (now [[GameFace fully vamped out]]) laughs and taunts Peter with the [[IronicEcho same words]]... only to stop and recoil as Peter, smiling, demonstrates that [[SkepticNoLonger he does now]].
** The ''Film/FrightNight2011'' remake did this too, except with Charley holding the cross instead of Peter. The vampire simply feigns weakness before grabbing the cross with one hand and pinning Charley to a car with the other. The cross catches fire as he touches it, but he blows it out without even flinching.
* ''Film/TheHauntingHour'' presents a rather twisted version of this by having The Evil Thing only exist as long as at least one person thinks about it, but making it almost impossible not to do so (if you'd read about a monster that vicious in a book, you'd think about it too.)
* In ''{{Film/Hook}}'', the grown Peter Panning says he doesn't believe in fairies. Tink 'faints', awakes, and tells him that fairies die when not believed in. The way she yells at him to clap harder seems to indicate that she's feeling just fine. (But then, she has a pack of Lost Boys believing in her.)
** Despite being the trope namer, this is actually something of a subversion. Tinker Bell says that a fairy dies every time someone says they don't believe in fairies; the statement seems to be all that is necessary regardless of actual belief. Similarly, Tinker Bell never mentions needing to believe to save her, just clapping appears to be enough.
* In John Carpenter's ''Film/InTheMouthOfMadness'', which pays homage to both Creator/StephenKing and Creator/HPLovecraft, we see just how terrible the consequences of this trope can really be.
* In ''Film/TheMatrix'' the red pill humans are able to perform seemingly superhuman feats by believing that they can do it, since they're in a virtual reality. As Spoon Boy elaborates: "There is no spoon." There are limits to even their abilities, though, which is what makes Neo, whose belief can transcend those limits as well, so important (at least, that's how it seems at first).
* Used at the end of the first ''[[Film/MightyMorphinPowerRangersTheMovie Power Rangers]]'' movie to repair their decimated hidden base and restore Zordon to full health.
* Parodied in the first film of ''Film/TheMummyTrilogy'' - Imhotep's soon-to-be [[SycophanticServant servant]] tries to fend him off with a cross and a murmured Lord's Prayer, which is utterly useless. He then runs through a keychain of similar holy symbols and their matching incantations, none of which have any effect until he yanks out a Star of David and starts babbling in Hebrew - which the undead priest recognizes as "the language of the slaves," which makes Beni useful to him as a translator. Discussion of the actual use of Hebrew slaves in ancient Egypt and the language they spoke at time is reserved for [[HollywoodHistory other places]]...
* In the JimCarrey vehicle ''Film/OnceBitten'', The Countess shrugs off the religious symbol ("Put down the cross, Robin. It only works in movies. Besides, I'm an atheist.") Then Mark shows up with a torch, and the Countess recoils, declaring, "Fire, on the other hand..."
* In the horror movie ''Film/TheSkeletonKey'', it is claimed the African witchcraft of Hoodoo can only be used on those who believe it. The plot plays with the notion that this means it's only psychology and suggestion (if you believe you were witchcrafted, you'll just act as if you did). However, the scientific approach is eventually abandoned. Once the antagonists finally manage to get the protagonist convinced that it's real, they can perform supernatural witchcraft on her. They then proclaim it's getting tougher for them to use witchcraft on new victims, as it's getting harder and harder to convince modern people that it's real.
* In ''Franchise/StarWars'', a Jedi's adeptness at manipulating the Force is closely linked to self confidence and belief in their abilities; sheer willpower and determination is not enough, and the Jedi must "unlearn" everything they think they know about how the universe works. In ''Film/TheEmpireStrikesBack'', Yoda blames Luke's failure to levitate his X-wing out of the swamp on his not believing that such a feat is possible.
* In ''Film/WesCravensNewNightmare'', a real supernatural entity tries to use the belief in and popularity of Freddy Krueger to manifest in the real world, adopting Freddy's identity. Creator/WesCraven (playing himself) explains that stories, and people's belief in them, have always been the bridge between the real world and the supernatural.
* Parodied in Creator/WoodyAllen's ''Film/WhatsUpTigerLily''.
-->'''Phil Moskowitz''': No bullets? Ah, but if all of you in the audience who believe in fairies will clap your hands, then my gun will be magically filled with bullets.
* [[http://en.wikipedia.org/wiki/Andrei_Tarkovsky Andrei Tarkovsky]] is fond of this one: ''Film/{{Stalker}}'' (not ''VideoGame/{{Stalker}}''), [[http://en.wikipedia.org/wiki/Solaris_(1972_film) Solaris]] (not [[http://en.wikipedia.org/wiki/Solaris_(2002_film) Solaris]]).
[[/folder]]

[[folder:Literature]]
* Subverted in F. Paul Wilson's ''[[Literature/TheAdversaryCycle The Keep]]'', in which a "vampire" ''pretends'' to be affected by a Christian cross, but not a Star of David in order to cause a Jewish professor to question his faith. [[spoiler:Later it's revealed that the vampire is actually affected by the symbol of a magical sword, and the Christian cross just happens to be very similar to this sword symbol.]]
* In Creator/NeilGaiman's ''Literature/AmericanGods'', gods and supernatural creatures are made real and powerful by worship and belief, and fade away and die when people stop believing in them.
* Laurel K. Hamilton's Literature/AnitaBlake novels also has this; if the person does not believe in the religious symbol, it will not work. To do with the beliefs of the person against the vampire.
* The page quote isn't the only example from Literature/TheBible: e.g., in the Gospels, Simon Peter walks on water until he starts to doubt.
** Creator/StephenColbert (apparently sincerely) believes this to be an instance of comic relief in the Bible, saying Jesus wouldn't be truly human if he could witness that without laughing.
* Subverted in ''Literature/{{Blindsight}}''; the vampires and crosses thing is [[DoingInTheWizard not because of anything religious or mystical]] but because their brains go into seizure [[WeaksauceWeakness when exposed to straight vertical and horizontal objects in their visual field forming a 90 degree angle]] (not as dumb as it sounds: there are people who have similar types of problems due to head trauma). That sort of thing is not that common in nature, and it wasn't much of a problem until their food source went and invented architecture and drove them into extinction.
* An early example: In Creator/AEVanVogt's ''Book of Pthah'' gods and goddesses are ordinary humans who have immortality and supernatural powers by the virtue of being worshiped by great numbers of the opposite sex.
* Creator/FredSaberhagen's ''BookOfSwords'' series had this as a plot development. The gods, including such familiar names as the war god Mars and Vulcan the smith, are bored. To entertain themselves, they play a game with humanity: 12 highly powerful magic swords are created, and spread throughout the lands purely to incite wars amongst the various nations. The plan backfires when, thanks to the highly visible power of the various swords, mankind's belief in the gods wane and is replaced by belief in the swords. Consequently, the gods rapidly weaken and die.
** In the interquel novel ''Ardneh's Sword'', which was written years later and is widely regarded as FanonDiscontinuity, it is explained that the Gods [[spoiler: Are really humans who put on some [[AppliedPhlebotinum Sufficiently Advanced Technology]] suits that turned them INTO gods]]. It seems likely that their apparent dependance on belief was psychosomatic at first, but became this trope over time.
* In JohnCWright's ''Literature/ChroniclesOfChaos'', this is one technique of FunctionalMagic, where the character can make true what he wants to be true. Its weakness is that he really has to want it; if you do not actually feel the malice necessary, you can not curse someone, for instance.
* C. S. Friedman's ''Literature/ColdfireTrilogy'' features a substance called fae which responds to brain activity and can do anything. This is used as a justification for FunctionalMagic as well as Clap YourHands If You Believe. A clever fae hack involved spreading a made-up religion in order to change the natural laws.
** Fae is also ''nasty.'' It doesn't just make for "proactive" magic; things based entirely on natural laws DON'T work if their user has any fear they might malfunction. Hear a bump in the night, and the fae will play on your instinctive fear to fill in what might have made it... The vicious cycle goes straight down into scenarios that approach CosmicHorrorStory. Furthermore, even the ''slightest'' belief that a device such as a gun could backfire will make it backfire; the fae makes Murphy's Law even worse. This is why the setting has been stuck in MedievalStasis for 1000 years at the series's start.
* In Creator/ChristopherMoore's ''Literature/CoyoteBlue'', this will happen to Coyote, and did happen to his brother [[spoiler:Anubis]], if people stop believing in him and telling his stories. Coyote fears this so much that he allows [[spoiler:Sam's girlfriend Calliope to die]] so that people will still talk about him.
* The Christopher Durang play ''Dentity Crisis'' references Peter Pan and the ensuing subversion from the fed-up actress playing Peter Pan who decides to sabotage it in the worst way possible:
---> That wasn't enough. You didn't clap hard enough. Tinkerbell's dead.
* The gods in the ''Literature/{{Discworld}}'' series work like this.
** The climax of ''Discworld/MonstrousRegiment'' involved [[spoiler:a beloved leader who had died and was being tormented by the prayers of those who put her on a godlike pedestal.]]
** In ''Discworld/{{Hogfather}}'', when the BigBad was magically preventing people from believing in the [[YouMeanXmas local equivalent]] of SantaClaus, the extra, unused belief-energy made any imaginary creature that was even slightly plausible (like a creature that eats odd socks, and a bird that eats pencil stubs) come into existence.
** ''Discworld/SmallGods'' describes in detail how gods come into existence and become powerful -and what happens when their followers lose genuine faith.
** "Belief" is stated as a very powerful force on the Discworld - if enough people believe something to be true, it will become true, however there are limits. The rules have never been fully stated, but it appears there needs to be a "space" that makes it somewhat reasonable such a thing could be true (hence the non-existence of the Give-The-Dean-A-Big-Bag-Of-Money goblin). In ''Discworld/{{Pyramids}}'' the mess of [[CrossoverCosmology multiple combined mythologies]] that made up the religion of Djelibeybi, much of which was self-contradictory, and a lot of which could be contradicted by simple observation, only became true when the kingdom was pushed into an alternate reality with an even lower reality threshold than the Disc.
** Mistress Weatherwax does this on many occasions, usually boxing the ears of said fairies. She doesn't believe in DEATH, because it's like believing in the postman.
*** Witches and Wizards generally take the same attitude about Gods. They ''know'' the Gods are there, so there's no call to go ''believing'' in them.
** An evil witch set herself up as secret ruler of the Magic Kingdom of Genua in ''Discworld/WitchesAbroad'' by manipulating the lives of people, and reality itself, by bending fairy tales around herself.
** In ''Discworld/CarpeJugulum'', one family of vampires have developed the ability to resist religious symbols (as well as most things that vampires are traditionally vulnerable to) through extensive psychological conditioning. [[spoiler:This later backfires when their conditioning wears off under the influence of a witch, but the study that went into it leads to them being able to recognize - and as a result be affected by - "hundreds of the damned holy things! They're everywhere! Every religion has a different one!"]]
*** Later expanded into the Black Ribbon Society, which provided a better integration with a multicultural modern city
** The ''New Discworld Companion'' has as Watch standard gear, "One holy symbol of recruit's choice, vampires, for the discouragement of. One Critique of Pure Reason, vampires, for the discouragement of (Freethinker's option)." This was before a vampire ''joined'' the Watch...
** What happens to people on the Discworld after they die is [[IronicHell determined by what they believe]]. Not necessarily what they want, but what they believe. In ''Discworld/SmallGods'', there is a character who believes in Om, but after he dies he thinks about what he believes and it's implied that he has a slightly different outcome than other Om believers. He has a different outlook on life than other Om believers, and therefore, something different would happen to him.
--->"What happens to people after they die is what they believe will happen. The people who go to hell are the ones who believe, deep down in their hearts, that they deserve it. However, if you've never heard of hell before, it's impossible to believe in it. [[SpoofAesop That is why it is important to kill missionaries on sight]]."
*** A group of people (the entire crew of a ship) who are assumed to be Omnians (as they live in Omnia) but know full well that it's all rubbish get a completely different afterlife from all the other Omnians. They decide to go looking for the afterlifes of those foreign gods they've heard of, where you get food, wine, and women for all eternity.
* By the time ''Literature/{{Dracula}}'' was written, vampire lore included an aversion to a cross. This, in different series, can be either the product of the vampire's belief in the cross, or the product of the wielder's belief in the cross. Often, it also works with another strong symbol of belief - for example, a rabbi using a Star of David to hold a vampire at bay. See: OurVampiresAreDifferent.
* The title character of ''Literature/TheDresdenFiles'' has little or no faith in the Almighty, so crosses don't ward off vampires for him. However, he has loads of faith in magic, and so his silver pentacle charm (a symbol of magic) works very well in putting aforementioned fang-faces in their place.
** His sometime ally Michael is a devout believer however, so the Cross works just fine, as does his named sword and since Michael is a Knight of the Cross his bare hands work equally well. (He's not called the Fist of God as a pet name, folks!) When a Red Court vampire (who are not as vulnerable to faith as the Black Court) mocks the idea that Michael's faith in the cross will defend him, she lightly places a finger on one of the crosses stitched into his cloak, and she instantly bursts into white flames.
** Faith in {{God}} himself is not necessary for a Knight of the Cross. Of the three knights presented so far, only Michael is particularly religious. Shiro was confused when he was being converted (though he tries his best to be a good Baptist regardless), Sanya is Agnostic [[spoiler:and Butters, the most recent Knight of the Cross as of ''Literature/SkinGame'', is Jewish]]. It's their belief in defending the common man against evil that gives the knights their powers. It just happens that in Michael's case, this belief manifest itself as Christian Faith.
** Dresden, being the FirstPersonSmartass he is, goes on to ''mock'' this trope during the climax of the fourth book, ''Summer Knight'', by charging into a Fae battle screaming '''[[CrowningMomentOfFunny "I don't believe in faeries!!"]]''' Doesn't help him kill any Fae any better, but certainly is good for the adrenaline.
** However, this apparently ''does'' work when fairies gain confidence in their own abilities: the more Toot-toot accomplishes on Harry's behalf, the bigger he gets. In the first book he is only six inches tall; by the 12th book, he is more than 15 inches tall and described as "ridiculously tall." Or alternatively, it was the result of [[GodsNeedPrayerBadly him becoming the leader of the "Za Lords" and gaining followers]].
** Magic in the Dresdenverse requires belief in whatever the caster is doing. A caster cannot produce a spell if they do not, deep down, believe in the reasons behind why they are casting the spell. This is actually a small but critical plot point in ''Turn Coat'', where [=LaFortier=]'s murder involved no magic being slung. It is eventually revealed that the killer [[spoiler:was being mind-controlled, but deep down she understood that she shouldn't be doing it, so she couldn't use magic against [=LaFortier=]. Meanwhile [=LaFortier=] knew she was being mind controlled and wasn't responsible for what she was doing, so he couldn't target her either.]]
** In the Novella ''Backup'', Thomas and Lara Raith are members of a secret society which fights against creatures who take their power from other people believing in them. The only way to assure victory is to limit as much as possible the number of people who know about the enemy (optimally: zero), making for some of the most severe "need-to-know" requirements ever faced by any army. (Being vampires, the Raiths aren't in it for the good of humanity, but rather to protect their food supply.)
** This trope is conversed in Literature/SkinGame. Harry and a member of his crew come across the [[spoiler: real shroud of Turin]]. When someone asks why the fake in the real world works like it does, Harry replies that if enough people believe the fake is real, it gains some power through said belief.
* In the ''Literature/{{Eisenhorn}}'' novel ''Malleus'', the title character is able to severely weaken [[ItMakesSenseInContext a Chaos-corrupted stone]] by recording himself reciting one of the (many) Imperial declarations of faith and continually transmitting the recording into the stone.
** In the third book ''Hereticus'', after Eisenhorn is forced to [[spoiler:release the bound daemon Cherubael]] in order to defeat [[spoiler:a Chaos Battle Titan]], he then tries to weaken him by reciting The Benediction of Terra. However by that point Eisenhorn has been both physically and mentally drained and couldn't force his will enough for the prayer to actually have effect. On the other hand, a crazed Imperial priest who witnesses all of this manages to scare off [[spoiler:Cherubael]] by mistaking him for a manifestation of the Emperor's power and running at him at full speed, chanting praises for the Emperor and holding a holy Imperial Aquilla, hurting [[spoiler:the daemon]] with the sheer force of his belief in the Emperor.
* In Creator/DavidEddings's ''[[Literature/TheElenium Elenium]]'' and ''Tamuli'' series, gods' powers are derived from their worshippers' belief. The Elene God is thus very powerful; the Younger Styric Gods have less individual power but together are considered comparable to the Elene God. Meanwhile, the Elder Styric Gods were severely weakened as a result of being forgotten to the point that all but one ([[spoiler:Azash, who found new believers in the Zemochs]]) were bound and sealed away. The Tamul gods, who are worshipped only superficially, end up manifesting as simple, childlike deities. Then there are the Forgotten Ones--gods without worshippers who are reduced to shapeless wisps with barely even a voice. Someone actually tries to depower a goddess by ordering the slaughter of her worshippers ([[spoiler:Zalasta, after he's been outed as a [[TheMole Mole]]]]), so the other Styric Gods each chip in some of their belief until the crisis is averted.
* The ''Literature/FactionParadox'' beings known as the Celestis are actually [[AscendToAHigherPlaneOfExistence ascended beings]] that are tethered in reality by nothing more than the power of others' belief in them; therefore, they appear as gods or demons wherever they choose to manifest.
* [[GoneHorriblyWrong Goes horribly, horribly wrong]] in regard to the "Stuff" in ''Literature/TheGoneAwayWorld'' by Nick Harkaway. It becomes not what you believe, but what you're ''thinking of''--and if you're thinking of ten things at once, it'll become a splice of all 10 things. This gets even worse if you [[TransformationTrauma get covered in Stuff]].
* ''Literature/GoodOmens'' not only explicitly uses this concept as the core of its magic system, but actually introduces a system which measures the intensity of belief in one of its footnotes.
* A variant occurs in the ''Literature/HaroldShea'' stories by Creator/LSpragueDeCamp and Fletcher Pratt, in which it's possible to travel to another world by believing in the logical principles that govern that world. The place you're going was real to begin with (even though [[AllMythsAreTrue they're all based on mythology or literature]]), but believing the right things makes it accessible to your senses.
* In ''Literature/TheHauntingOfAlaizabelCray'', there's an interesting case: [[spoiler:when humanity believed that disaster was God's anger, everything was fine. Then came the beginning of the Age of Reason, and we [[OutgrownSuchSillySuperstitions outgrew such silly superstitions]]... or so we thought. Because we had no-one left to blame, but lacked the emotional maturity to take responsibility for our actions, our subconscious minds started to blame ''every fairy-tale-style monster ever'', at which point they appeared and began to terrorise the world's cities.]]
* In ''Literature/IAmLegend'', vampires fear the holy symbol of what they believed in before they became vampires. The Protagonist's archenemy is terrified by the Star of David.
* In the ''Literature/IronDruidChronicles'', all gods and supernatural entities are created by human belief and thought, including Jesus, the Celtic gods, the Norse gods, Elvis Presley and the comic book version of Thor.
* In Creator/StephenKing's ''Literature/{{IT}}'', the eponymous shapeshifting monster takes the form of a werewolf, making it vulnerable to silver simply because the child heroes of the book firmly believe that werewolves ''have'' to be vulnerable to silver. Also, believing that his inhaler was full of poison allowed a protagonist to harm It with the contents.
** Established in King's writing much earlier in his short story ''The Boogeyman'', which is in many ways a precursor to ''IT''.
** A cross does not work on a vampire in ''Literature/SalemsLot'' because its owner has lost his faith. When that character faces vampires again in a later King book, he has recovered his faith and is able to (briefly) drive them off, even after he puts the cross aside - it's only a symbol, after all.
** It should be noted that disbelief in the supernatural generally doesn't protect against it in King's works. For example, in ''Literature/It'', the eponymous [[RealityWarper reality-warping]] [[VoluntaryShapeshifting shape-shifting]] monster devours victims regardless of whether or not they believe in the supernatural, but strong enough belief in supernatural things (like, the fact that silver bullets can be used against It when It takes the form of a werewolf) allows the protagonists to fight back. Also, in the short story ''1408'', the hotel manager urges Mike Enslin, a writer of books that chronicle his sojourns in supposedly haunted locales, not to stay in room 1408 specifically because he ''doesn't'' believe in the supernatural, and things will go worse for him because of it.
* Deconstructed in ''Literature/KingdomKeepers''. Enough people believing in them is what causes several {{Disney}} characters to come to life...including the villains, who are putting the world in danger.
* This appears to be the driving force behind mythological beings in the ''Logical Magician'' series of books by Robert Weinberg. In the second book, an Amazon (naturally, exceedingly beautiful) serving as a weapons instructor is explicitly confronted by the main character with theories regarding the rather hideous appearance of historical amazon women; he's rebuffed with "Maybe the real ones were. We aren't." Applies to myths both old and new; one of the most feared mythological beings around is 'The Man'. Also given an interesting inversion; [[spoiler:Nergal, the Babylonian god of disease, has been hauled into the modern world. With no believers to get rid of, he seems invincible, until the main character gets an article about him published in several supermarket tabloids. Since people automatically disbelieve what they read in those, this does Nergal in.]]
* AllMythsAreTrue in Creator/DouglasAdams's ''Literature/TheLongDarkTeaTimeOfTheSoul'' because of this effect. The old gods, like Odin, are languishing but a new [[spoiler:God of Guilt]] is created, possibly from society as a whole, but also possibly from the eccentricities of Dirk Gently alone.
** ''Franchise/TheHitchhikersGuideToTheGalaxy'' has a theory on God's non-existence as a guide entry. Shortly, it goes like this: Since nothing as useful as the Babelfish can be born through coincidence, this proves God's existence, but with knowledge, there isn't faith, and without faith, God is nothing. This seems to follow the same logic.
* [[http://www.gutenberg.org/files/7477/7477-h/7477-h.htm Lord Dunsany]] uses this. To say where would spoil an excellent short story.
* Some gods in Steven Erikson's ''Literature/MalazanBookOfTheFallen'' are formed from the belief of their adherents and die if they are forgotten. Others are independently existing beings whose divine powers are powered by worship.
* In ''Literature/MonsterHunterInternational'' holy symbols have power over undead monsters by virtue of the belief placed in them. However, the biggest act of [[HolyHandGrenade faith-based ass kicking]] comes from [[spoiler:Milo, who shares the author's Mormon beliefs]].
* Skeeve from ''Literature/MythAdventures'' is struggling to teach his apprentice Massha to light a candle via magic when he realizes she doesn't actually believe she's capable of such a thing. When he encourages her to visualize a magical trinket (a form of magic she ''does'' believe in) inducing the same effect, she succeeds in setting the candle alight.
* A rare inversion with a short story ("Obstinate Uncle Otis") about an obstinate Vermonter (and as such, the most obstinate man in the world) whose power of disbelief was legendary, to the point where he could almost convince others that their eyes were tricking them. And then [[LightningCanDoAnything he got struck by lightning]], and got a dose of [[YourMindMakesItReal Your Mind Makes It Reality]]. The statue in the town square to the man he hated? Gone after he commented about how "No one would build a statue to a nincompoop like that!" The barn that was obstructing a nice view? Also gone when he commented how "No barn there, boy! Nothing but th' view - finest view in Vermont." His nephew realizes the danger this poses (e.g. his hatred of UsefulNotes/FranklinDRoosevelt, his recent disbelief in stars, etc.). It comes back to bite the elderly man on the ass, though, as he got a bit of EasyAmnesia and believed himself to be a traveling salesman with a different name. "Humph - ain't no such person as Otis Morks."
** And before FridgeHorror enters into it, the narrator was ''also'' named Otis Morks, yet didn't disappear - unlike his hapless, obstinate Uncle.
--> '''Narrator:''' The ancient prophets may have had faith strong enough to move mountains. But Uncle Otis was possessed of something far more remarkable, it seemed - a lack of faith which could ''un''move them.
* Creator/TomHolt spoofed this scene in ''Open Sesame''; a fairy provides medical care by shouting "I do believe in humans!" And again in ''Paint Your Dragon'':
--->''There's an urban folk-myth that every time a human says he doesn't believe in dragons, a dragon dies. This is unlikely, because if it were true, we'd spend half our lives shovelling thirty-foot corpses out of the highways with dumper trucks and the smell would be intolerable.\\
There's an old saying among dragons that every time a human says he doesn't believe in dragons, a human dies, and serve the cheeky bugger right.''
* Trope namer comes from a famous scene from ''Literature/PeterPan''. In this [[TheVerse verse]], a fairy is mortally wounded any time a child says "I don't believe in fairies;" in the scene in question, Peter uses the effect in reverse to save the fairy Tinker Bell's life by calling on children everywhere to indicate that they ''do'' believe in fairies. (In the original stage version - which predates the novel and the various film and television adaptations - this was an audience participation bit...and, in case you're wondering, if the audience is a bunch of heartless bastards who won't clap, the orchestra is instructed to begin the applause.)
* Subverted in Christopher Golden's ''Shadow Saga'' in that the effects of the cross on vampires is purely psychosomatic because [[spoiler:the Roman Catholic Church captured a bunch of vampires during the dark ages and brainwashed them into believing in a number of myths.]]
* The basis of all magic in the ''Literature/{{Shannara}}'' series.
* In ''Literature/SsaliaAndTheDragonsOfAvienot'', the only way to reach the upper shelves in the jade tower's (physics-defying) library is to walk on thin air, which can only be done if one believes such a feat is possible.
* In Creator/SergeyLukyanenko's ''[[Literature/TheStarsAreColdToys Star Shadow]]'', it is eventually revealed that the human [[FasterThanLightTravel jump drives]] work because the pilots believe them to work. This is also why humans are the only ones who retain their sanity when using it - because this should not be possible. The protagonist even recalls that the jumper was invented by a bunch of underfunded Russian researchers, and the scientific basis for the device was added as an afterthought and seems tacked-on. Also, every jumper works exactly the same, no matter the design or power. Kinda makes sense since astronauts have to believe they'll succeed in order not to die.
* In Christopher Stasheff's ''Literature/WarlockOfGramarye'' series, the planet Gramarye has a native fungus known as "witch-moss" which can assume animated forms based on the thoughts of those with latent PsychicPowers. Since five centuries of inbreeding has spread those genes to half the population, a lot of fairy tale creatures have since become real; if they become ''too'' real, and there's some of both genders, they can even mate and have fixed-form offspring, essentially creating a whole new species. The Wee Folk were born this way and can somehow interbreed [[HalfHumanHybrid with humans]], producing ''[[YouFailBiologyForever fully fertile offspring]]''.
* Interestingly used in Jeri Smith-Ready's ''Wicked Game''; Ciara Griffin's blood heals her vampire boyfriend of holy water scars, which are supposed to be permanent, and Ciara postulates that it's because of her complete ''lack'' of religious faith.
* In explaining the history of money Creator/DaveBarry specifically uses the Tinker Bell scene as an analogy for how money works these days (i.e. no longer tied to gold or another precious metal). We all believe currency has value, so it does.
* There is a short story in which a demon has the job of dragging humans to Hell, and can only be defeated by holy words. The specific religion doesn't matter so much as the strength of the person's belief. His first intended victim is a Christian who prays and forces him to let go. The second is an atheist, and ''her'' holy words are the laws of physics. HilarityEnsues.
* In ''Literature/{{Pact}}'', this effect is [[JustifiedTrope justified]] by the animist nature of the setting. Small, barely perceptible spirits are everywhere, and as a result of years of tradition, have been convinced to enforce the various laws that bind practitioners, such as that they CannotTellALie, by removing power from those that break the laws. The spirits like a good show, and if you can look good while doing something and are as showy as you can be and convince ''them'' that you can manage something, then it's more likely that you'll pull it off.
[[/folder]]

[[folder:Live Action TV]]
* In ''Series/BeingHuman'', vampires recoil from George's Star of David pendant. But George's affection for his best friend Mitchell (who is a vampire) makes Mitchell immune to its deleterious effects. Mitchell even keeps the necklace safe when George [[WolfMan transforms]].
* In one episode of ''{{Bottom}}'', Richie and Eddie are saved from a Ferris Wheel [[DeusExMachina by the hand of]] {{God}}. When they remember that they don't believe in God, the hand vanishes and they fall to their doom.
* In the ''Series/BuffyTheVampireSlayer'' episode "Out of Sight, Out of Mind," a girl is actually rendered invisible because no one ever noticed her (an effect heightened by the school she attends being built over a hellmouth).
* Possibly occurs in TheStinger of an episode of ''Series/CarolineInTheCity''. During the episode's plot, Caroline and others make references to Caroline's [[GirlfriendInCanada made up boyfriend]]. In the stinger a man claiming to be her boyfriend appears; the episode leaves it the audience to decide if it was Richard playing a joke on her, or if she accidentally talked him into existence.
* In ''Series/{{Community}}'' episode "[[Recap/CommunityS2E06Epidemiology Epidemiology]]" it was brought up and then thoroughly subverted.
* Toyed with in ''DeadLikeMe''. The recently deceased will cross-over with the gateways to the next world taking a form that appeals to them. In the pilot, a little girl sees a huge spectral carnival; in a later episode, the soul of an old yet feisty man of [[strike:indeterminate UK]] clearly Irish origin leaps from the precipice of [[strike:a chalk cliff]] the Cliffs of Dover.
* ''Series/DoctorWho'':
** [[Recap/DoctorWhoS29E13LastOfTheTimeLords The finale]] of the ''Series/DoctorWho'' new series third season came under some fire for relying on this, albeit with a HandWave involving a {{Phlebotinum}}-assisted telepathic field that focused the belief, causing what fans call [=TinkerBell=] [[CrystalDragonJesus Jesus]] or Fairy Doctor.
** In the [[Recap/DoctorWhoS31E13TheBigBang fifth season finale]] [[spoiler:the Doctor was erased from existence, but Amy remembered him and somehow magically brought him back.]] It... ''sort of'' [[ItMakesSenseInContext makes sense in context.]]
** The Doctor once cobbled together a temporary ''working'' TARDIS out of spare parts, lampshaded by a companion that he accomplished this feat partly because he refused to even entertain the possibility that he couldn't.
** Earlier, in [[Recap/DoctorWhoS26E3TheCurseOfFenric "The Curse of Fenric"]], a cross works only if the bearer has faith in it, and other objects of faith work equally well: a WWII Russian soldier fends off vampires with a soviet badge, and both the Doctor and Ace are able to hold them at bay with no physical object, through their faith in each other. The priest who doubts his meets sticky end.
* One episode of ''Series/FraggleRock'' introduced a one-off character named Skinfred, a small monster whose [[EmpathicShapeshifter transformations]] were based upon this Trope. His physical appearance depended on ''what other people thought about him'' (it's impressive how upbeat his personality was given how very definitely BlessedWithSuck he was). Red and Wembly like him, think he's very cute and friendly... and that he sports goofy pigtails. Ma Gorge does ''not'' like him, thinks he's creepy and scary for living in her flooded basement, and wonders if he's actually a giant, fanged, two-headed monster. Guess what happens next. (Skinfred: "Aw, I '''hate''' having to be a monster!")
** A similar creature appeared in the ''FraggleRock'' comic book. The cast had to deal with a considerably less friendly monster who was also exactly as tough as an opponent believed it to be, resulting into hilarious scenes of our heroes making things worse and worse.
---> "I don't care if you're fifty feet tall..."
---> '''Poof!'''
---> ''(Monster is now fifty feet tall.)''
* In the TV miniseries ''Film/{{Merlin}}'', Merlin finally defeats the evil Queen Mab by encouraging everyone to ''forget about her''. This is the culmination of the fading belief in her and led to her vanishing. The novelizations went as far as noting that Merlin omitted her from his stories about the events and misattributed them to Mordred or Morgan le Fay.
* On BBC ''Series/{{Merlin}}'', when Arthur is [[spoiler:trying to draw Excalibur]], Merlin says that he needs to truly believe he can in order to do it. Subverted since Merlin was just trying to boost Arthur's confidence: once Arthur is sold on Merlin's story, Merlin covertly uses magic to make the task extremely easy for Arthur, thus reinforcing the idea he was trying to instill.
* [[DiscussedTrope Discussed]] in ''[[Series/TheOfficeUS The Office]] (US)'': Nellie tells the office that she can't make their wishes come true (i.e. give them all raises) unless they believe in her (i.e. accept her as the manager just because she [[BavarianFireDrill walked in and asserted that she was now the manager]]). This ends with her comparing herself to Tinkerbell and making everyone clap for her.
* ''Series/PowerRangersMysticForce'': The key component to being able to use magic is, it seems, believing in magic. In the premiere, Nick is unable to use magic because he doesn't believe - even after he's seen others using it (and despite considerable effort 'trying' to believe). He gains the ability to cast spells only after announcing that he really does, after all, believe in magic. In the finale, the entire city's belief is used as a CombinedEnergyAttack.
* The ''Series/StargateSG1'' BigBad of seasons 9 and 10, [[SufficientlyAdvancedAlien the Ori]], are [[AscendToAHigherPlaneOfExistence ascended beings]] who thrive on worship. [[GodsNeedPrayerBadly And they also ''lose'' their powers when not worshiped,]] [[spoiler:hence how The Ark Of Truth beats Adria, forcing the Priors to realize that the Ori, and by extension, Adria herself, were ''not'' gods.]] A fitting end.
** The {{Big Bad}}s of the previous eight seasons, [[AGodAmI the Goa'uld]], are a more figurative example. Once a significant number of people stop believing that a particular Goa'uld is a god, it's usually a sign that said Goa'uld is about to lose out.
* An episode of ''Series/StarTrekTheOriginalSeries'' has the crew find a pulled-from-myth planet of Ancient Greece, presided over by Apollo, who laments that the rest of the gods perished, more or less, from a lack of followers.
** The StarTrekExpandedUniverse has "the Beings" in Peter David's ''StarTrekNewFrontier'' series, who gained power from worship and fear, and inverted when it turned out the most powerful among them was so because he gained power from peoples' belief in ''themselves''. In the novel ''Gods Above'', the only way for the crew to defeat them is to be truly fearless.
* An early ''Series/StarTrekTheNextGeneration'' episode had a SufficientlyAdvancedAlien known as [[EveryoneCallsHimBarkeep The Traveler]] strengthened by the entire Enterprise crew concentrating on making him better. (Granted, they were in an area of the universe where [[SpaceIsMagic thoughts become reality]], but it still fits the trope).
* The early ''Series/StarTrekDeepSpaceNine'' episode "If Wishes Were Horses" had the contents of people's imaginations becoming real, starting with Rumpelstiltskin, courtesy of Miles O'Brien reading the book to his four-year-old. The low point was Julian Bashir's fantasies of Jadzia Dax resulting in a copy of the latter that kept throwing herself at him. Meanwhile Odo manages to wish Quark into a holding cell. After they imagine a spatial anomaly nearly destroying the station they figure it out and Sisko orders everyone to stop speculating and focus on the hard data. [[spoiler:Turns out there were SufficientlyAdvancedAliens experimenting on them to find out what imagination was.]]
* An episode of ''Series/{{Supernatural}}'' focused on a spirit that was created (and maintained) by people's belief in it. Unfortunately, getting people to ''stop believing'' was not an option.
** Leading Sam to wonder how many of the things they hunt only exist because people believe in them.
** One episode had a kid who made things he was afraid of real because he believed in them. He turned out to be TheAntichrist, which made him a RealityWarper.
* Lettie Mae, Tara's mother, in ''Series/TrueBlood'' gets rid of a "demon" that makes her an alcoholic via exorcism. It turns out to be a scam, but that doesn't faze Lettie Mae.
** This also works on Tara as well, for a while, at least. Then she finds out it was all a scam and becomes her old "friendly" self. Then a maenad shows up and tells Tara it was her belief that called her to Bon Temps.
* One episode of ''WireInTheBlood'' dealt with this trope. The murderer of the story was thought by some people to be using magic. Tony Hill, however, knew that it was all in the victims' heads and when the murderer was finally caught, she thought Tony was a powerful wizard because he'd been able to see through her "invisibility".
* Nickelodeon's ''Kids Choice Awards 2008'' has a character called the Rocktopus (a rock and roll octopus who wears shades) and during the end where Jack Black and Orlando Bloom are doing the final slime stunt - there's no slime coming out at first because the machine ''requires someone with 8 arms to operate it'', and the Rocktopus happens to be the one that fits that - the only problem is that he needs encouragement from the audience - so the audience give him encouragement by shouting... "Slime! Slime! Slime! Slime! Slime! Slime!"
* Creator/StephenColbert fully believes in this trope, naming it Wikiality, wherein if enough people believe something to be fact, it is; and the best method for altering the public's belief in something? Change its Wikipedia page.
** To demonstrate this, he single-handedly tripled the African Elephants' numbers via Wikipedia. Quite a feat.
[[/folder]]

[[folder:Music]]
* The song ''Kingdom of Heaven'' of the Dutch symphonic metal band ''Epica'' has a chorus that is this trope (see RealLife below too): ''Quantum physics lead us to. Answers to the great taboos. We create the world around us. God is every living soul.''
[[/folder]]

[[folder:Newspaper Comics]]
* ''{{Garfield}}'': Jon Arbuckle reads a newspaper story about a man who thought he could fly if he put on a superhero cape and jumped from the top of a skyscraper - but then [[DownerEnding the paramedics peeled his corpse off the street with a spatula]]. Cue Garfield running past Jon, also wearing a cape, headed for the edge of the table, claiming that the dead man obviously didn't have enough faith. [[FridgeLogic (Of course, it's much easier to have faith if you don't have nearly as far to fall.)]]
[[/folder]]

[[folder:Professional Wrestling]]
* During one storyline in the early-to-mid-nineties Kama stole TheUndertaker's urn of power. TheUndertaker said that he now had to rely on his [[FanCommunityNicknames Creatures of the Night]] (his special nickname for his fans) to provide him with the power he needed to win the match.
* According to "American Made", HulkHogan's theme song in {{WCW}} pre-FaceHeelTurn (1994-1996), ''you'' are what makes Hulkamania possible: "He wears the heart of his country on his sleeve / He'll fight for your freedom if you really believe."
[[/folder]]

[[folder:Tabletop Games]]
* ''Beyond the Supernatural'' features a reversal of sorts with the nega-psychic class. Most character classes in this game have psychic and/or magical abilities. The nega-psychic has psychic powers, but is so convinced that supernatural phenomena are bunk that his power is used unconsciously to suppress all psychic and magical phenomena in his area. For example, a character who can normally lift things with telekinesis will find it difficult or impossible to do so around the nega-psychic, thus bolstering the nega-psychic's belief that there is no such thing as telekinesis.
* In ''TabletopGame/{{Deadlands}}'', this device works in both short and long term. When visiting the SpiritWorld of the setting, exactly what one sees is colored by exactly what one expects. A Protestant might see Mount Zion, with Heaven at the top and Hell at its base. A Native American might instead see a [[TheWorldTree World Tree]], again with pleasant things at the top and bad things at the bottom. And most of the "Abominations" in the game world are drawn straight from people's worst fears; sometimes, a house is haunted not because someone died horrifically there, but because people ''believe'' it is haunted.
* The {{Defictionalization}} of ''Webcomic/DresdenCodak''[='=]s ''[[TabletopGame/DungeonsAndDragons Dungeons and Discourse]]'' takes place InAWorld like this filled with philosophers. The upshot is that they can do things like use their belief in Cartesian duality to do two moves in one round.
* The ''TabletopGame/DungeonsAndDragons'' campaign setting ''TabletopGame/{{Planescape}}'' revolves around the idea that belief shapes the planes. It can also move mountains, as the beliefs of the inhabitants of an area determines it's actual geographic location.
** Exploited several times in the video game ''PlanescapeTorment''; for example, the player at one point unlocks a memory of a previous incarnation who had just debated a man into the conclusion that he did not exist, which caused him to vanish.
** The concept was added to the ''TabletopGame/ForgottenRealms'' setting in the "Avatar trilogy" of novels. As of Third Edition, this is actually considered the default handling of gods in the default setting (Greyhawk, though they don't call it that) and ''Forgotten Realms''; in ''Literature/{{Dragonlance}}'', suiting the role of its gods, although belief is important to them, it's not directly necessary for their existence.
** In ''TabletopGame/{{Eberron}}'', the gods exist independent of mortals entirely, but their power in the material world seems to be dependent on their worshipers - as in, the stronger churches are better able to carry out what they divine as the will of their god... though different religions don't even agree on whether or not that is even necessary. It isn't even strictly made clear that the gods actually ''exist'', or whether the manifestations and abilities of priests and so forth are just a (local) result of their faith. And some of the things that are worshiped as gods (such as the Dreaming Dark) don't really fit any conventional use of the term.
** The book ''Faiths of Eberron'' makes this trope even more evident. Followers of the Lord of Blades (A warforged of considerable might, but who is mortal) have access to divine magic from their belief/faith in ''his'' divinity and his cause.
** In the 3.5 core rules, clerics were able to gain power by revering a cause. ''TabletopGame/{{Eberron}}'' actually had attempts to train clerics of ''nationalism'' (although it failed... except in [[PathOfInspiration Riedra]]).
** The 2E supplement ''Shaman'' used this trope extensively, with the twist that any spirits generated by such power of belief weren't considered "real" by deities, or at least, not as "real" as the deities themselves.
** ''TabletopGame/{{Ravenloft}}'', like ''TabletopGame/{{Eberron}}'', prefers to keep its gods' legitimacy subject to doubt. At least one of the major deities of the Land of Mists, Zhakata, is ''expressly stated'' to be the figment of a crazy darklord's twisted imagination. This doesn't prevent clerics of Zhakata from receiving divine spells when they pray. (However, it is also stated that their spells are granted by Ravenloft itself, rather than what they believe.)
** Inverted with two spells of the Illusion school, ''phantasmal killer'' and the even more powerful ''weird''. These spells create incredibly convincing illusions in the mind of a victim of his greatest fear that can literally cause him to die of fright. The only way to fight it is to realize it isn't real and have enough willpower to "disbelieve" it (whether a victim can succeed or not depends on a lot of factors, including his Wisdom score and how powerful the wizard casting it is).
* In ''TabletopGame/{{Exalted}}'', gods, ghosts, demons, and most supernatural beings (including the Exalted) regain Essence and Willpower faster if enough people pray to them. In Yu-Shan (Heaven) these prayers coalesce into Quintessence and Ambrosia, substances that are the most delicious food and drink in the history of every and are easily transmuted into... anything else, making anyone who has even small amounts fabulously wealthy.
* ''TabletopGame/GeniusTheTransgression'' features something of an [[InvertedTrope inversion]] with Bardos. When enough people believe in something, and then suddenly ''stop'' believing (like, say, if it's publicly disproven), the energy of all those minds changing their opinion releases Mania into the world. This has created, among other things, an underground world full of dinosaurs, an army of Martian invaders, and a race of Aryan "[[TheUbermensch Übermenschen]]" of genuinely superhuman ability.
* Similar to the Doctor Thirteen example mentioned above, one power available to players in ''{{GURPS}} IOU'' is the advantage Mundanity. Magic and super-science fails to work in a Mundane's presence, and at the higher levels monsters, aliens and assorted other non-normal entities actually change to have mundane explanations (a monster turns into someone wearing a monster costume, the alien invasion turns into a movie set) until the character leaves the area.
** A lesser version of this is available in the 4th edition as the perk (one-point advantage) Skeptic. Any supernatural powers the character doesn't believe in get a penalty to use, and the effect is cumulative when there are multiple skeptics present.
* In ''TabletopGame/InNomine'', the Marches, the land of dreams separating the corporeal realm (Earth and the rest of the physical universe) from the celestial realm {Heaven and Hell) is populated by the power of human imagination with pagan gods and creatures of myth.
* The card game ''TabletopGame/{{Munchkin}} Bites'' has an item ''The Yarmulke of Religious Obfuscation'' which gives the wearer an extra bonus against ''The Vampire Hunter'' and ''The Meddling Cleric''.
* In the ''TabletopGame/NewWorldOfDarkness'':
** In ''TabletopGame/MageTheAwakening'', the disbelief of normal humans ''can'' unravel magic, but only because their souls bear a fragment of the nothingness which stands between the sources of magic and reality.
** In ''TabletopGame/ChangelingTheLost'' a magical effect preys on the beliefs and psychological expectations of mortals and other supernaturals to make Changelings and Fae Tokens appear as mundane people and objects, rather than the (sometimes flagrantly) magical things they are.
** Elsewhere in the TabletopGame/NewWorldOfDarkness, spirits of things reflect what people ''believe'' that thing should be -- a dog spirit, for instance, is nearly the platonic ideal of a dog -- but it's left deliberately unclear whether this is because human belief shapes spirits, or spirits shape human belief. Is a spider spirit the way it is because we believe a spider should be this way... or do we think spiders should be this way because this is how spider spirits are?
* In the ''TabletopGame/OldWorldOfDarkness'':
** In ''TabletopGame/MageTheAscension'', reality is the result of consensus belief; normal humans who haven't pierced the {{Masquerade}} can disrupt magic through disbelief. "That can't happen," they think, and their belief is strong enough to ''make'' it unhappen, make them forget it ever happened, and punish the mage for his attempt. Conversely, mages have carefully-constructed belief systems that allow them to impose their wills upon reality and reshape it as they see fit. For example, the Earth never used to orbit the Sun, steam power never used to be possible, until the Technocracy managed to make most of humanity believe in it.
** In ''TabletopGame/HunterTheReckoning'' the collective force of human belief makes supernatural phenomena simply invisible to most people.
** ''TabletopGame/ChangelingTheDreaming'' had this as a central element of the story; since humanity considers fairy tales to be, well, fairy tales, changelings consider themselves to be an endangered species, and the discouragement of freedom and the imagination (known as Banality) is actually ''toxic'' to them.
** ''TabletopGame/VampireTheMasquerade'', vampires aren't averted by crosses or other holy symbols unless the wielder's faith is particularly strong. In addition, a vampire character may purchase a number of supernatural flaws that are common to vampire lore: be it being repulsed by crosses, being unable to cross running water, being unable to enter a house uninvited... Depending on the DM and player's interpretation, those flaws are either factual problems caused by the character's particular bloodline (after all, ''someone'' must have given rise to those myths, and that someone probably sired other vampires) or this trope: the vampire fears garlic, because he's convinced vampires do.
** The demons in ''TabletopGame/DemonTheFallen'' power their abilities through the harvesting of faith from humans. This can be done quickly, through "reaping" (kind or cruel as the demon wishes), or on a long-term basis by making a pact with a human.
* In ''TabletopGame/OverTheEdge'', one NPC mentioned is a fairly obvious {{Expy}} of [[http://en.wikipedia.org/wiki/James_Randi James Randi]], who makes all the rampant weirdness of the setting shut down around him due to sheer power of disbelief.
* In ''TabletopGame/{{Scion}}'', the various deities (and their progeny, including the player characters) derive power from the number of people who are aware of their exploits. This is known as Legend. However, while the Gods make sure stories about them maintain circulation, they discourage outright ''worship'', because Fate is a ''bastard'' when it comes to such strong connections. It's a dangerous balancing act.
* In ''TabletopGame/{{Shadowrun}}'' (fourth edition, at least), there are numerous magical traditions based on assorted religious and philosophical beliefs, but all are equally capable paths to studying magic. In addition, spirits take on the shape of whatever the caster believes they should take the shape of; a spirit of fire can look like everything from a triumphant archangel to a happy little puff of flame depending on who summons it.
* In ''TabletopGame/{{Toon}}'', things like gravity will only work on you [[GravityIsAHarshMistress if you remember that it should]]. As a result, you can take a Smarts test hoping to fail, and if you do, you can cheerfully row across the sea with a boat that's still tied up at the dock, or make a call from a phone in the middle of the Wild West...
* This is the basic principle in which magic in ''TabletopGame/UnknownArmies'' works. An Adept's obsession warps their view of the world so much that he can bend reality with his will simply because he is absolutely sure that what he does is possible.
* Da Orks in ''TabletopGame/{{Warhammer 40000}}'' subconsciously generate a mild psychic field, its strength directly proportional to the amount of "boyz" present, so if enough Orks believe in something then reality is given a swift kick in the balls and told to follow the proper, Orky way of doing things. While it won't cause a stick to be able to shoot bullets if an Ork believes it will, Ork belief in "[[LawOfChromaticSuperiority da red wuns go fasta]]" really ''does'' make vehicles painted red move slightly faster, and because Orks believe that [[LargeAndInCharge the biggest Ork is in charge]] an Ork will ''actually grow'' in response to other Orks following him.
** While Orks can't make a stick fire bullets, their powers are able to make a lot of things that shouldn't work shoot bullets. Most of their "shooterz" are little more than boxes filled with gears and bullets that are in the general shapes of guns, and Orks have been known to make ships without fuel fly across solar systems.
*** The power of the Ork gestalt field varies DependingOnTheAuthor. In one book, an Ork with a huge {{BFG}} took on an entire Imperial Guard platoon. When the Ork was killed by a sniper and the gun was recovered, it was found to have no trigger or firing mechanism, making it little more than a metal pipe with a gun belt fed through it. In [[Literature/CiaphasCain another]], Ork weapons and vehicles ''can'' be used by human forces fairly effectively, but they are still prone to misfires and jams. Ork Mekboyz have a very good instinctive understanding of mechanics, but for the most part, Ork technology requires the gestalt field to work.
*** In one of the Gaunt's Ghosts novels, the eponymous commissar has no problems commandeering an ork buggy beyond the fact that it was designed for a significantly stronger being and as such lacks power steering. Another example is that of a unit of Ork-hunter Imperial Guard who will often loot Ork guns and use them, again with no problems. The general idea is that Ork technology does work, and the Orks' psychic power simply makes it work better.
*** This sometimes even works against the Orks. Their mortal enemy [[Characters/Warhammer40000ImperialGuard Sebastian Yarrick]], despite being as badass as a human could possibly be in the horrifying 40K universe, REALLY should be dead just by weight of age and everything he's endured making his body give out, even with advanced future medicine. But he's accomplished so much against the Orks that they believe he's an unkillable monster, ergo...
** Tech-priests of the [[MachineWorship Adeptus Mechanicus]] ''are'' taught genuine mechanical skills, just in an odd and highly-ritualised way involving lots of chanting and application of holy oils in order to please the "machine spirits". Machine spirits are quite real, with many examples of a vehicle functioning long after its crew are dead, or even "going feral" and rampaging across the battlefield. It isn't certain how much of Imperial technology is this trope and how much is genuine engineering.
*** The holy oils could just be lubrication for various components and the chanting is in binary, it might be some sort of voice activated diagnostic program.
** There are also the faith-based powers of the Adeptus Sororitas (aka Sisters of Battle), particularly in ''TabletopGame/DarkHeresy'', where their Faith renders them immune to the negative effects of Daemonic Presence, and provides many other useful abilities at higher character ranks.
[[/folder]]

[[folder:Video Games]]
* Specifically referenced in ''VideoGame/AFineDayForReaping'', as an explanation for why you can't simply walk past an armed soldier. As TheGrimReaper, you'd normally be ImmuneToBullets... but you only exist because of this principle, and combined with the soldier's firm belief that there's no problem he can't solve by shooting it, he might actually be able to kill you.
* In ''VideoGame/AgeOfMythology'' and the Titans expansion, all four civilizations need their followers to do something for them before they'll grant units and upgrades. However, simply advancing your civilization gives you one free God Power to use at your discretion, so advance today!
* The science-magic dichotomy in ''[[{{Arcanum}} Arcanum: Of Steamworks and Magic Obscura]]'' is partially based on this; an extremely science-oriented character is immune to magic because s/he does not believe such foolishness could have any tangible effect.
* How deities in ''VideoGame/AsurasWrath'' gain the power of mantra. Or they can just kill you and take your soul, that works too.
* In the PC game ''VideoGame/BlackAndWhite'', the various deities gain "faith points" when humans witness them doing things; one can convert villages by building up enough faith points. Also, godly powers are driven by belief, which is gained from getting villagers to worship at your temple.
* In ''CityOfHeroes'', the Clockwork King's robots shouldn't work at all, but because he believes they do-- [[JustifiedTrope thus subconsciously animating them with his telekinetic powers]]-- they do.
* ''VideoGame/FinalFantasyTactics'' uses this as an actual game mechanic, where characters have a numeric stat called Faith between 0 and 100, and this is directly applied to damage amounts and success rates of magic that the character uses or is hit by. A character with a Faith stat of 0 is utterly immune to magic. Characters' Faith stat can be raised or lowered with certain abilities, though if you raise faith high enough, a character will become too pious to put up with your obsession over mundane trivia like trying to stop demons from taking over the world, and will wander off to worship God in peace.
* The Eidolon Wall in ''VideoGame/FinalFantasyIX'' reveals that the Eidolons are in fact created by the belief of humans. The creatures of myth and legend in effect become real by people believing them, and serve as guardians of the planet.
** So apparently they watched an episode of ''{{Transformers}}'', leading to the creation of Ark, the TransformingMecha Eidolon.
* Many magical items in ''VideoGame/TheGameOfTheAges'' turn out to contain no intrinsic power, but your initial belief in them imbue them with actual magic.
* GloryOfHeracles does this to Iphicles [[spoiler: who was given a fragment of Heracles's soul to be revived from the dead. He gets amnesia from the experience and believes himself to be Heracles. When Iphicles learns the truth, that he's actually dead, he fades into ether.]]
* In ''VideoGame/KingdomOfLoathing'', the description of "Trusty", the axe wielded by the Avatar of Boris, uses this trope to explain how certain legendary weapons become legendary.
-->Not every magical weapon is forged of meteorite iron under an unusual planetary conjunction, inscribed with gilded runes of ancient power, and imbued with supernatural strength and sharpness through mystical rites and sorcerous incantations. In truth, many of the most powerful weapons of lore are possessed of far humbler beginnings — common metal, torn from an enemy's grasp in a dire emergency. If the warrior survives the day, the weapon will likely be kept. Polished, sharpened, and re-sharpened, it will be carried from battle to battle, becoming as much a part of the man as his own arm, and as his name rises from warrior to hero to legend, so too will an aura of reverence and awe begin to surround the blade. Legend and belief are powerful forces, and it should be no surprise that a powerful artifact might have become powerful simply by dint of everyone believing it to be powerful. That is, after all, where the gods came from.
* ''VideoGame/{{Mother}}''
** In ''VideoGame/{{MOTHER|1}}'', [[spoiler: Giegue]] is defeated by the use of the [[spoiler: Sing command, singing Queen Mary's lullaby]] that Ninten and friends learned over the course of their adventure.
** In the fangame midquel ''[[VideoGame/CognitiveDissonance Mother: Cognitive Dissonance]]'', Alinivar has to use PK Harmony to defeat Giegue/Giygas. [[spoiler: It puts your party into "Harmony" status, until Niiue goes into "Giygas" status, showing he's finally returning to Giegue to normal... For awhile. Niiue thanks you for using it at the end of the game.]]
** In ''VideoGame/{{Earthbound}}'', the only way to beat the BigBad Giygas is the liberal use of the "Pray" command... and the prayers of everyone who you met on your quest, culminating in ''the player''. [[TheFourthWallWillNotProtectYou These prayers actually do physical damage to him.]]
* The main character of ''VideoGame/{{Okami}}'' is a severely weakened god reincarnated as a wolf. She gains experience points in the form of "faith" and grows stronger as she helps people and performs miracles. [[spoiler:The final battle actually sees her stripped of all her powers a second time, and it's only because of her left-behind ally spreading her name and leading the people of Nippon to pray to her that she's able to regain them all and save the day.]]
* The ''[[OsuTatakaeOuendan Ouendan]]'' and ''EliteBeatAgents'' series run entirely off this, in which members of a Japanese cheerleading squad (or secret government agency, in the case of EBA) show up and miraculously resolve random peoples' issues through, well, cheering and/or interpretive dance. This is taken to its logical extreme in each of their final story missions, where everyone's fighting spirit takes on a more, uh, [[CombinedEnergyAttack tangible form.]]
** Ouendan's [[spoiler:destroys an asteroid about to collide with Earth.]]
** EBA's [[spoiler:crushes an alien invasion.]] Bonus points for featuring the cast actually clapping their hands because they believe. "[[CrowningMusicofAwesome I WAS BOOOOOOOOOOORN IN A CROSSFIAH HURRICAAAAAAAAAAAAANE]]"
** Ouendan 2's ''[[spoiler:reignites the dying sun.]]''
* Subverted in ''PhantomDust.'' It's explained in a [[AllThereInTheManual small codex entry]] that Faith skills are, confusingly enough, not powered by faith, but a lack of faith. The NPC who uses the most faith skills is appropriately suicidal and self-loathing, having no faith in herself or her comrades.
* The law of physics upon which all of reality is ordered in ''PlanescapeTorment''. The game is set in the outer planes, a multiverse created from the accumulated belief of the people living in the real world (the "Prime Material Plane"), so this operates both on a grand scale (every version of Hell believed in by all of the world's cultures exists somewhere) and a smaller one (in the Planes, one can will a plant to grow or create a person by telling enough people he exists).
* A key point in the ''Franchise/ShinMegamiTensei'' series, where entities from [[AllMythsAreTrue virtually every mythology ever]] exist, specifically because people believe in them.
** The [[VideoGame/{{Persona 2}} second installment]] of the spinoff ''VideoGame/{{Persona}}'' series takes this to far greater extremes, where rumors you start [[InfallibleBabble actually become true]].
* The is the general fandom consensus towards how ''Franchise/SilentHill'' works; the DarkWorld and the monsters therein are manifestations of a character's fears, memories, et cetera; the MalevolentArchitecture is someone willing the player character not to succeed, and the player character receives weapons and ammunition from their desire to live and achieve whatever goal they're working towards. As the game continues and all people concerned become more desperate and determined, the difficulty level and the potency of available weapons increases. This also explains why the mysterious "power" is limited to the eponymous town, as only a small cult there believes in it... until the more recent games, that is.
** The film makes this somewhat canon. [[spoiler:The little girl's hatred, combined with that of a spirit of vengeance, transforms the town into a hell. In turn, the cult it was created to punish is protected by their faith; more precisely, it's their blind ignorance of their own fate which prevents the spirit from killing them all (until it finds a loophole).]]
* ''SpaceChannel5 Part 2''. The game has people you save helping you stop evil by singing and dancing along. But the trope really comes into play [[spoiler:in the final level, where Ulala falls unconscious and defeated, but the entirety of the cast starts to clap for her and bring her back, before they all sing in unison to stop the bad guy. Even though just moments before she was zapped close to dead.]]
* ''[[VideoGame/TearsToTiara2 Tears to Tiara 2]]'': [[TheHero Hamil]] raises the battle cry of Ashtarte, and all Canaanites at the Ba'al Festival follows suit. This empowers Tarte, which prevents both her and Hamil from being burnt alive.
* ''VideoGame/{{Touhou}} Fuujinroku ~ Mountain of Faith'' works around this concept, as the BigBad is forced to flee to Gensoukyou after the normal world [[GodsNeedPrayerBadly loses faith in her, making her powerless]].
** While only gods need faith, ''belief'' is hugely important to the setting. Youkai (most of the cast) are created from humans ascribing the mysterious to unknown forces, and will fade away if people stop believing in them. Since this has mostly happened, the setting is behind a barrier that causes it to be sort of the opposite of the rest of the world, pulling in things that people don't believe in.
* Used during the final boss battle of ''ViewtifulJoe 2''. Joe and Silvia go into the real world to fight the BigBad, but find out [[FridgeLogic their powers don't work, yet his do.]] After getting thoroughly beaten, the crowd starts to chant their support, at which point, the two of them transform, and hand out a royal beating of their own.
* In ''VideoGame/WorldOfWarcraft'', the ability to use the [[WhiteMagic Light]] comes from the belief of the individual--for this reason, non-sentients who lack free will are unable to use it the conventional way, crises of faith such as disasters can often have the side effect of cutting off individual contact, and people who commit atrocities can still access the Light if they believe they are acting for the greater good.
[[/folder]]

[[folder:Web Comics]]
* The [[TheFairFolk Fae]] kingdom in ''DanAndMabsFurryAdventures'' works on belief, while the laws of physics take a day off. Scientist-by-heart Jyrras, then proceeds to [[http://www.missmab.com/Comics/Vol_799.php step right through a floating platform]].
* In ''Webcomic/{{Digger}}'', this can have some disturbing results. In particular, street children put a new spin on a CrystalDragonJesus, making his mother evil. This creates a goddess so horrible that just seeing her drives a priestess insane, and apparently leaves the priestess covered in "shadows" that are not her own. The evil goddess is based on myths created and believed by street children in Miami.
** Gods cannot die while their followers believe in them, even if they want to.
* ''Webcomic/DreamCatcher'' does it for laughes as a bonus page [[http://dreamcatcher.smackjeeves.com/comics/604884/the-next-page-o/ FAN SUPPORT POWER BOOST!]]
* In ''ElfLife'', magic is portrayed as only having an effect on those who believe. [[http://www.elflife.com/d/20000917.html Knowing this doesn't seem to help.]]
* In ''{{Fans}}!'', the "crosses are only effective in the hands of those who believe" rule is used as an indication that a particular character's faith is wavering. In desperation, one of the fans (Rikk, a Christian whose faith had been weakening at the time) instead tries a symbol he ''does'' believe in: the Vulcan salute. It works, [[spoiler:but not really; the vampire was faking it.]]
* ''Webcomic/GunnerkriggCourt'': Coyote is of the opinion that human belief created every supernatural entity, and is even capable of re-writing reality.
* Played with in [[http://www.machall.com/view.php?date=2003-04-21 this]] ''MacHall'' strip.
* In ''Webcomic/TheOrderOfTheStick'', Elan creates his own god, Banjo the puppet ([[DontExplainTheJoke so called because he has a banjo]]) for when he multi-classes to Cleric. When Roy tells him his opinion, Elan calls for Banjo to smite Roy. A tiny storm appears and throws a tiny lightning on Roy, which has no effect. Elan comments that maybe Banjo needs more believers.
* This is the entire plot of ''ParallelDementia''.
* ''Webcomic/{{Roommates}}'' never outright tells us, but heavily implies that fan belief and human memory keeps fiction alive and has a cast of [[MediumAwareness self-aware]] fictional characters. The examples include things like characters, who [[TheScrappy fans would rather forget]], being DeaderThanDead, or a DangerouslyGenreSavvy character telling his son to fight for his love/happiness, beacause then ''someone'' will believe and even if he fails or even dies he will be remembered and so live and get new chances.
** And now with the AnthropomorphicPersonification of Disbelief in the picture this pretty much became fact. Also a "Clap if you believe" reader poll [[http://asherhyder.deviantart.com/journal/poll/3317784/ here]] to combat him.
* Art from ''Webcomic/SequentialArt'' loses the ability to use any piece of technology, once he's told that "artists radiate an anti-technology energy... and the effect gets 100 times worse when the artist knows of the energy's existence."
** Eventually, he has surgery to correct it, which involves hypnotic therapy, a computer chip, and a large drill. [[spoiler:It's a placebo, but that doesn't stop it from working.]]
*** Later, he tells Pip to whack him on the back of the head to disable the chip, bringing back his imaginary powers temporarily.
* In ''Webcomic/SluggyFreelance'', the following exchange takes place during the first clash with vampires:
-->"You'll also need a holy symbol to drive him back in case he's too strong for you!"\\
"Will this can of beer work?"\\
"Is it light beer?"\\
"Nope."\\
"That should do the trick."
* [[BuiltWithLego Legotech]] in ''Webcomic/TroopsOfDoom'' runs on this. If you can make an agglomeration of Legotech vaguely resembling the device you want, ''it will function perfectly as such''.
* ''UnwindersTallComics''. [[http://tallcomics.com/?id=108 Here:]]
-->'''Howard:''' Excuse me. All of the women at that table would like to meet you.\\
'''Dr. Minivan:''' A-Are you sure? How do you know?\\
'''Howard:''' You must speak with them! Your doubt is causing them to fade away!
* Webcomic/{{Wonderella}} once used "Peter Pan fairy logic", as she called it, to get people to bring Christmas strength back to TheKrampus. It worked, and he was able to return to his job of... throwing naughty children in a sack and taking them to hell.
* In ''ZebraGirl'', magic works along these lines. As one character explains, Magic fundamentally doesn't work, but as long as you don't believe that it does. For example the main magic user tells a character to close his eyes as the magician heals him because as long as his eyes were open he wouldn't be able to accept the spell working. This same wizard then starts on a one man (but occasionally one werewolf) mission to bring back magic into the world through teaching people (mainly kids) to believe in it again. He does this as a really, really, really, good street magician.
* Weirdly used in ''WebComic/EightBitTheater'' [[http://www.nuklearpower.com/2004/12/11/episode-490-going-up/ #490]]. [[{{Cloudcuckoolander}} Fighter]] manages to defy gravity because he thinks the team broke physics, causing [[HeroicBSOD Red Mage's brain to crash]].
--> '''Fighter:''' Don't you understand? With gravity slain, now we can fly! ''(floats off the top of the panel)''\\
'''Thief:''' Huh.\\
'''Red Mage:''' But he. You can't. Love, hate, clouds. ''(faints)''
[[/folder]]

[[folder:Web Original]]
* Most of the monsters of ''[[http://bogleech.com/animations.html The Fear Hole]]'' are created by human fears in an alternate dimension. This is mostly PlayedForLaughs.
* GaiaOnline's ill-named "Demonbusters" event in 2009 ends with the titular gods depowered and turned into humans. The following Christmas event had them getting Gaians to believe and pray to them so they could become divine again. [[spoiler: [[SubvertedTrope It didn't work.]]]]
* ''FanFic/ImAMarvelAndImADC''. When {{Deadpool}} runs out of bullets he asks the audience to do this to make new bullets appear in his guns. When this doesn't work he calls the audience a bunch of amputees.
* In ''WebVideo/{{Kickassia}}'', the Website/ThatGuyWithTheGlasses team [[note]]Including those not in Nevada at the time[[/note]] attempted an amazing one of these to [[spoiler:ressurrect Santa Christ]], complete with appealing to every member and many lapsed members of the site, and eventually asking the audience to join them in [[spoiler:wishing Santa Christ back to life]]. At the end of this, Santa Christ proceeds to... [[spoiler:[[{{Anticlimax}} lie there dead.]] But he comes back after three days anyway.]]
* ''WebOriginal/ProtectorsOfThePlotContinuum'': The [[http://starshadowhall.tripod.com/ppc/menu.html Substance Menu]] has this to say about [[BrainBleach Bleeprin]], a medication made of bleach and aspirin: "Please refrain from reminding the [=PPCers=] that this is chemically impossible. They already know that. They don't care. However, if you remind them, it may no longer work; then they will probably kill you."
* Wiki/SCPFoundation: this is how [[RealityWarper SCP-239's]] power works. If she believes something to be true, then reality instantly reshapes itself so that her beliefs ''are'' true. The fact that she's an 8-year-old who's aware of her power, but not how it works, makes things... [[MikeNelsonDestroyerOfWorlds problematic for the rest of humanity]].[[DangerouslyGenreSavvy The Foundation]] tried to convince her that she is a witch and can only cast spells out of "spellbooks", and although this failed to limit her power, it made her much easier to enroll in [[SecretGovernmentWarehouse "magic school"]]. [[spoiler:She's in a coma now thanks to her powers [[RealityWarpingIsNotAToy backfiring]]. She was so afraid of Doctor Clef that she believed he was planning to kill her. The belief became reality, which was bad since Doctor Clef also happens to [[MageKiller specialize]] in killing Reality Warpers like 239.]]
* [[WildMassGuessing One fan theory]] states that this is how [[TheSlenderManMythos Slender Man]] exists; the reason he scares people and gets them to keep records of him in pictures and videos is so he will exist forever.
* In docfuture's hilarious "LetsPlay ''Sonic2SpecialEdition''," in [[http://video.google.com/videoplay?docid=1149863216010157450&hl=en# Mystic Cave Zone]], he points out that the game engine is belief-based, and consequently the graphics looked bad because not enough of the viewers believe that this game exists.
* The inverse occurs in [[WebVideo/TheSpoonyExperiment Spoony]] and [[WebVideo/AtopTheFourthWall Linkara's]] review of ''[[Comicbook/{{Warrior}} Warrior #4]]'', when they realize that the comics' ability to break hypertime and merge the universes is powered by their desperate attempts to believe in or discern [[MindScrew any sort of meaning]] from the comics. They then call for all the critics to help them defeat the Warrior by declaring how much they…''don't'' care.
* ''TabletopGame/TechInfantry'' borrows the explanation of the magic of Mages from the TabletopGame/OldWorldOfDarkness, so it follows this trope. One of the characters even tries to ''weaponize'' this fact of life, using a MindControlDevice to change what everyone believes about how the universe works, and thus change the way the universe actually works.
* ''Roleplay/WeAreOurAvatars'': To a limited extent, Luna's technology works like [[{{TabletopGame/Warhammer40000}} Orc Tech]], if she believes the red car will go faster the red car will go faster. This does not however give her the ability to make a stick work like a gun just because she thinks it is one.
* {{Discussed}} by Blog/WorstMuse: "If the rights to your favorite character haven't entered the public domain, it's because you didn't believe hard enough."
* In the ''WhateleyUniverse'', there are two different kinds of MadScientist. The first are Gadgeteers, who operate based on the laws of reality, obey them, and just have a strong enough understanding of sane science that they can leap years ahead of everyone else. The second are Devisers, who simply ''believe'' strongly enough in their inventions that, somehow, those inventions work. A particularly strong Gadgeteer is a threat. A particularly strong ''Deviser'' is one shade away from a full-fledged ''RealityWarper''.

[[/folder]]

[[folder:Western Animation]]
* In ''WesternAnimation/AaahhRealMonsters'', it was the fear and belief of monsters in the minds of humans that caused them to come into existence in the first place, and they can only exist if humans continue believing in monsters, which is why they scare. In one episode the entire cast begins to disappear because they hadn't been scaring enough humans, and reform themselves after going on a scare rampage.
* In ''WesternAnimation/BarbieAndTheDiamondCastle'', while a song is the key to the castle, the lyrics indicate that it's belief in the song that actually makes the castle appear. "Believe/Your song will hold the key"
* In the ChristmasEpisode of ''WesternAnimation/BuzzLightyearOfStarCommand'', it's the power of belief that allows [[SantaClaus Santa's]] sleigh to work (naturally, the final dose of necessary belief-power comes from Team Lightyear's [[TheCynic most skeptical]] member, XR).
* Ember, a ghostly rocker from ''WesternAnimation/DannyPhantom'', gets more powerful the more her fans chant her name.
* Parodied in an episode of ''WesternAnimation/EarthwormJim'' where, after his super-suit gets stolen, Jim tries various generic ways of gaining super powers (including space radiation and radioactive arachnid bites). One of his attempts is to plead to the audience where he tells the viewer he will get powers if the audience were to "Believe! Believe and clap very hard!" prompting:
-->'''Jim:''' ...Well? Are they clapping?
-->'''Peter:''' A few of 'em, [[SelfDeprecation most of them]] [[WhoWouldWantToWatchUs are just changing the channel]].
* Inverted in one episode of ''WesternAnimation/TheGrimAdventuresOfBillyAndMandy''. Mandy is unharmed by the Tooth Fairy's wand (which can turn people into AnthropomorphicFood) because she doesn't believe in the Tooth Fairy. (Or course, this was not only a DreamSequence, it was Billy's dream sequence; [[CloudCuckooLander He has weird dreams.]])
* Mocked in ''WesternAnimation/{{Futurama}}'':
-->'''Bender:''' If you don't believe in him, he can't hurt you!\\
'''Santa:''' ''(smack)''
-->'''Bender:''' Oh GOD, the pain!
* One episode of ''WesternAnimation/{{Freakazoid}}!'' spoofs the ''Peter Pan'' example above, with Cosgrove asking the viewers to revive a defeated Freakazoid with their applause.
-->'''Cosgrove:''' ...And throw in some [[InherentlyFunnyWords "Huggbees"]] while you're at it.
-->'''Crowd:''' HUGGBEES!
* In the ''WesternAnimation/JusticeLeague'' series from the early 2000's: Franchise/WonderWoman, despite being super strong, sometimes exclaims "Hera give me strength!" Which maxes her strength out to the point where it rivals Franchise/{{Superman}}'s She even states that there were times that without her belief in Hera, she would not have been successful.
* In an episode of ''WesternAnimation/TheRealGhostbusters'', the city was visited by two benign ghosts who appeared to be Sherlock Holmes and John Watson, and a very ''nasty'' one who appeared to be Professor Moriarty (who eventually conjures up a demonic version of the Hound of Baskervilles). Egon at first thought this didn't make sense; as fictional characters, these people were never alive to begin with, and thus could not be ghosts. When it became clear that they were indeed the real deal, he brought up a theory he had read about called "belief made manifest". What this meant was, if enough humans believe that a fictitious character is real and he has enough fans, it can give the character a pseudo-life, which seems to be what happened. Once they figured this out... The game was afoot!
* In ''WesternAnimation/SouthPark'', the Imaginationland storyline revealed this to be the case (technically DoingInTheWizard in doing so). Everything and everyone ever imagined by someone on Earth is real in [[MagicalLand Imaginationland]], including all religious figures (even including real people believed to be gods and prophets, such as Joseph Smith, founder of the Mormon faith). This is made hilarious if one remembers that Jesus has a public access television show in the real world.
* Inverted in ''WesternAnimation/TeenTitans'': Recently-deceased villain Slade has returned to beat the living crap out of Robin... or so Robin thinks. Turns out he'd been exposed to a drug that makes him see Slade, and his body to [[YourMindMakesItReal react as if struck]]. He is able to disbelieve in his opponent just in time to save himself from the killing blow.
* An episode of ''WesternAnimation/TinyToonAdventures'' revealed that laughter (or, perhaps more correctly, the Power Of Fandom) helped cartoon characters stay young.
* In ''WesternAnimation/WinxClub'' the Believix transformation's powers are amplified when humans believe in the Winx.
[[/folder]]

[[folder:Other]]
* A classic joke has a beautiful woman trying to drive a vampire away by brandishing her crucifix; the vampire's response is an amused, "Sorry, lady, 'svet gornisht helfen" (Yiddish for "It won't help a bit").
* In ''{{Roleplay/Apotheosis}}'', miracles run on this. If a god's followers believe something, then (assuming the god is strong enough) said god will gain it as a new miracle.
* The Indian deity Hanuman, the "monkey god," is so caught up in his devotion to Lord Rama that he needs his followers to remind him of his own divinity for his powers not to dwindle.
* "The Law of Attraction" and "Universal Magnetism" and "Like Attracts Like" are concepts explored in at least two books, ''The Science of Getting Rich'' by Wallace Wattles and ''Excuse Me, Your Life is Waiting'' by Lynn Grabhorn, as well as at least two films: ''Literature/TheSecret'' by Rhonda Byrne (also a book) and ''What the Bleep'' by J.Z. Knight. Both films feature followers of Ramtha's School of Enlightenment in Washington State, which also teaches this concept.
** A lot of megachurches have co-opted this by calling it "prosperity theology".
* The LogicalFallacy known as ''argumentum ad populum'' implies this. For some reason that doesn't stop people from using it, even though the implications should be obvious.
* Somewhat related: SantaClaus is often depicted as "real for those who believe."
* There is a joke about some Jews coming to a rabbi and asking him if he can pray for a rain. He says it won't work since they have no faith. How does he know they have no faith? They didn't bring umbrellas.
* There's a number of urban legends about Christian college students and their Atheist professors, who try to convince their students that God isn't real. One variation has the professor hold up a piece of chalk saying that if God was real, he'd stop the chalk from breaking on the ground if he dropped it. The student prays that he will have the courage to tell the professor he believes in God. When he tells the professor this, the chalk slips out of the professor's hand, rolls down his pant leg, bounces off his shoe, and lands on the ground unharmed.
** The professor's retort, if someone is around to say it to the original storyteller, goes something like "I've been doing this for twenty years. Either we have a coincidence, or 1/20 of a god."
** Countered with 'God doesn't do cheap tricks for show'. Which means it was dumb luck the chalk didn't break.
** Another version has the professor standing on a chair declaring that if God exists, he should knock him from the chair. Followed by a student bodily tackling him and [[TheScourgeOfGod claiming he was sent because God was busy.]] Obviously, [[DontTryThisAtHome trying that in real life easily leads to legal and academic problems.]]
* This is a common feature of New Age beliefs in general. In Wicca and some other Neo-Pagan religions, a variant is taught: you can perform magic(k) by visualizing the desired results and focusing your will upon them, but doubts in the efficacy of the technique will rob you of the necessary focus and prevent it from working.
** Some practitioners of magic(k) claim that any symbol has the power the magic(k)ian invests in it. This can lead to two conclusions: One, the whole subjectivist interpretation (the idea of all persons living in a reality of their own making (thus not the same as the one everyone else lives in), or two, that humans actually innately possess some huge magic power, but have developed mental blocks to prevent the world's destruction by a toddler EldritchAbomination, and such symbols are ways around these psychic walls.
* This is generally how the occult practice of chaos magic works -- if someone believes in it, you, too, can believe in it, and channel it for power. GrantMorrison, being delightfully wacky, has written articles on channeling the occult significance of everything from the [[ClassicalMythology Greek pantheon]] to the NewGods to Film/JamesBond.
* [[http://www.youtube.com/watch?v=eyqUj3PGHv4 WE'RE GONNA YES SO HARD, WE'RE GONNA BRINK KIKI BACK TO LIFE. BELIEVE IN THE YES.]]
* Generally invoked by psychics, fortune-tellers and such chalartans when they fail to perform during controlled experiments. Many of them would argue that the general atmosphere of skepticism around them is suppressing their powers.
[[/folder]]

[[folder:Real Life]]
* Celebrities. If you don't put faith in a celebrity... if you don't "clap your hands"... the celebrity will disappear!
* For that matter, most superstitions work this way too; believing something may encourage someone to try things and do things they might not otherwise. Like athletes who tend to have the most unusual and personalized superstitions.
** ConfirmationBias also plays into it. If you do a superstitious ritual or action, and something "good" comes of it (or at least nothing "bad"), you attribute it to the superstition. Likewise, if you forget to do the superstition, and something "bad" happens, even if it was probably a coincidence, you'll still attribute it to the lack of the superstition.
* [[http://en.wikipedia.org/wiki/Moore%27s_paradox G.E. Moore's eponymous Paradox]] asserting that something is true ''demonstrates one's belief'' that it is true. It's kinda like screaming in a rage ("I'M NOT ANGRY!").
* [[http://notalwaysright.com/ah-managers/1229 An argument]] in Website/NotAlwaysRight involves this trope when a customer seeks a blue camera and no such item exists in stock, so the manager plays along in order to get the customer to buy a red one.
* Pat Robertson [[http://www.rawstory.com/rs/2013/04/01/robertson-god-gives-less-miracles-to-too-educated-americans-who-learn-science/ claims]] that the credulous will get more miracles than the skeptical.
* The placebo effect is the real life equivalent of this, though it is far more effective in fiction than in real life. This is generally attributed to the nervous system and the immune system being interconnected, and the idea that the immune system can be activated in a specific part of the body. The effect is strongest when treating symptoms with a strong mental component, like pain and nausea.
** It's pretty strong in real life too. There is one instance of rats apparently being tricked into curing themselves of a certain type of cancer by a placebo. (They were given normal water, then the real stuff in flavored water long enough to cause remission, then normal water again long enough for the cancer to cease going into remission, then flavored water without the chemo.)
** And it's getting stronger. More recent drug trials have been seeing larger and larger parts of the placebo control group actually having positive reactions. This is mostly chalked up to people having a much stronger belief in modern medical pharmacology, and hence are more likely to believe the placebo is really a new miracle drug.
** There's also the related [[http://en.wikipedia.org/wiki/Nocebo nocebo]] effect which has been claimed as powerful enough to kill people.
** And then things get really interesting and weird: [[http://www.guardian.co.uk/science/2010/dec/22/placebo-effect-patients-sham-drug The placebo effect can happen even when people are TOLD it's a placebo!]]
*** That, in itself, may be a placebo effect, as the people were told that the pills they were taking were indeed placebos...that have shown to have markedly improved their health anyway. The people believe that despite the pill being a fake, maybe there's something in it that really isn't fake!
*** It likely has more to do with the fact that people know placebos work. If it works it works, it doesn't matter if it's fake.
* Quantum Mechanics (or [[ArtisticLicensePhysics a misinterpretation of it]], especially the part which indicates that mere observance changes the outcome of an event), is often used as a HandWave for any and all of the above. However, this [[http://en.wikipedia.org/wiki/Consciousness_causes_collapse#Criticism is not a mainstream or even accepted interpretation for quantum mechanics except for a tiny minority]], and the entire ''point'' of Quantum Mechanics in the first place is that subatomic particles behave completely differently to larger matter.
** Incidentally the reason why observation changes objects on the quantum level is that the only way to observe any subatomic particle is to collide it with another subatomic particle. It has nothing to do with consciousness changing the reality, as subatomic particles collide anyway all the time.
* The stock market. Expectations of the future are one of the most powerful forces, as evidenced by how stocks consistently rise/fall after optimistic/dour speeches, reports and addresses. So if the market tanks, it will come back to life if everyone just believes in it.
** Bank runs, where people believe that their bank is failing and rush to take their money out of it, which causes more people to believe that the bank is failing, which causes more people to take their money out of it, which eventually causes the bank to actually fail, even if the original reason for thinking that that the bank was failing was completely false.
** Really, ''money itself'' depends on this trope. Money gains or loses its worth only based upon widespread belief in it (specifically, the faith the holder has in his ability to exchange it for something he really wants like food, which is dependent on the other guy with the food having enough faith that he can in turn use that money to trade for something else like clothes, and so on). Currency that could be used to buy quite a lot one day can be next to worthless the next, in the right circumstances. The money itself hasn't changed, the little squiggly world leader imprinted on it hasn't changed; its value derives entirely from how widely it is believed to have value.
* This is how hypnotism works. You have to ''believe'' that you can be hypnotized in order for it to work, and it is impossible to be hypnotized against your will. The fact that the word "hypnotism" is applied to a half-dozen or so completely unrelated ideas, some well-understood and some utterly absurd, doesn't help.
** In addition, even if you believe you can be hypnotized, you cannot be commanded to do things you are unwilling to do consciously. A man might be able to be hypnotized into thinking an orange is a apple, but if he believes stealing is wrong, there is no way you can force him to take money out of a wallet without permission.
*** Theoretically he can be made to believe that the wallet is his own, but this depends on the skills of the hypnotist and the susceptibility of the subject.
* This is the most likely explanation of the Midnight Game. The environment and the setup mean the player(s) will spend three and a half hours stressing, worrying, and freaking themselves out.
* Some more modern branches of the occult (In particular, Chaos Magic)follow this line of belief. The idea is that while the magic itself might not be real, the belief in it is very real and may be able to 'trick' your mind into believing that it is real (For example, curses only working if the victim feels like they've been cursed, and therefore would begin to associate every little misfortune with the curse so that, in their mind at least, they have been cursed).
* Invoking this trope is an advised method of avoiding The CentipedesDilemma: If you believe you will be successful in a task you already know how to do, you are not likely to overthink the actual process and goof yourself up.
[[/folder]]
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