History Main / ClapYourHandsIfYouBelieve

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-->-- '''UsefulNotes/{{Jesus}}''' addressing his disciples, [[Literature/TheFourGospels Luke 17:5-6]]

** Dresden, being the FirstPersonSmartass he is, goes on to ''mock'' this trope during the climax of the fourth book, ''Literature/SummerKnight'', by charging into a Fae battle screaming '''"I don't believe in faeries!"'''. It doesn't actually do anything , but certainly is good for the adrenaline. Knowledge of fairies does matter just like everything else, though, as Mab made sure the Brother Grimm published books of Fairy tales to ensure that humans continued to know about them. And on a smaller scale, the more authority Harry has give Toot-toot and the more he accomplishes, 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. [[GodsNeedPrayerBadly Him becoming the leader of the "'Za Lord's Guard" and gaining followers]] actually results in him personally becoming more powerful.

** 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. And not even what they ''think'' they believe; as noted above, most Omnians in ''Small Gods'' don't really believe in Om, but we see a couple of them in the AntelifeAfterchamber, and it seems like they only ''realise'' this at that point.

** In ''Literature/{{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.

** 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 ''Literature/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.

** 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.

* The player character of ''[[VideoGame/ChoiceOfGames Choice of the Vampire]]'' is only repelled by crosses and hallowed ground if they believe they will be -- or, [[MaybeMagicMaybeMundane perhaps]], if they ''don't'' [[FightOffTheKryptonite believe]] they ''won't'' be.

* ''VideoGame/SlayThePrincess'': This is [[spoiler:the true nature of the relationship between the Player and the Princess. Everything about the Princess changes depending on how you, the Player, see her and what actions you take. For example, when you first visit the cabin, you have the option to take the blade on the table. If you do, indicating that you are willing to slay the Princess, the Princess will be a dangerous and arrogant prisoner. If you don't take the blade, the Princess will be a demure and innocent damsel. In either case, your action becomes justified. This is because the Player and the Princess are the Long Quiet and the Shifting Mound, [[AnthropomorphicPersonification the manifestations of stability and change respectively]]. It's in her nature to change form. ]]

* ''Series/TheTwilightZone1959'': In "[[Recap/TheTwilightZoneS5E132NinetyYearsWithoutSlumbering Ninety Years Without Slumbering]]", Sam Forstmann is convinced that he will die if his grandfather clock, which was given to his parents on the day that he was born, ever winds down as his father and grandfather had always told him as much. He becomes so obsessed with winding the clock that his granddaughter Marnie Kirk and her husband Doug send him to a psychiatrist named Dr. Mel Avery. Shortly afterwards, Sam collapses when the pendulum briefly stops swinging. Several weeks later, Sam's spirit appears to leave his body after the clock winds down. However, he has come to realize that Marnie, Doug and Dr. Avery were right all along. He tells his "spirit" that he doesn't believe in him and therefore he doesn't exist. Sam then tells Marnie that when the old clock wound down for the last time, he was born again.
* ''Series/TheTwilightZone1985'': In "Room 2426", Dr. Martin Decker is extremely skeptical of his cellmate Joseph's claim to be able to [[{{Teleportation}} teletransport]]. Joseph assures him that he has been specifically trained and has done so many times. He explains that a person must believe that they are capable of teletransportation in order to do it. [[spoiler: {{Subverted|Trope}} in that Joseph is a [[TheMole mole]] who tricks Martin into believing that they have teletransported to a safehouse. [[DoubleSubversion Double Subverted]] in that, after realizing the truth, Martin uses the power of his mind to transport himself to safety.]]

* The player character of ''[[Creator/ChoiceOfGames Choice of the Vampire]]'' is only repelled by crosses and hallowed ground if they believe they will be -- or, [[MaybeMagicMaybeMundane perhaps]], if they ''don't'' [[FightOffTheKryptonite believe]] they ''won't'' be.

*** Domains in the Temenos -- the DreamLand of humanity's collective subconscious -- are populated with "extras" that suit the local theme, such as generic nameless passers-by in an urban landscape. They usually have no real personality and [[WelcomeToCorneria minimal interactivity]], but if visitors treat one like it's real, it slowly becomes more unique and free-willed, possibly reaching a point where it becomes a person in its own right.

* The fact that people's beliefs influence how they act, and by acting people can create things, means that in a very real way the belief in something can cause in to come into existence. The effect is generally much more subtle than it is portrayed in fiction however. And the opposite is almost as likely: there are many many cases of people inventing something in the process of trying to prove that thing ''wouldn't'' work. It is also true that people do not necessarily act on their beliefs, but are in fact very susceptible to social pressures: so it's relatively rare for this trope to occur even in it's subtle form in real life. However, many modern technologies were first conceptualized in science fiction and then became reality almost solely because someone read the story and decided they were going to figure out how to make that cool thing a reality.

*** Domains in the Temenos -- the DreamLand of humanity's collective subconscious -- are populated with "extras" that suit the local theme, such as generic nameless passers-by in an urban landscape. They usually have no real personality and [[WelcomeToCorneria minimal interactivity]], but if visitors treat one like it's real, it slowly becomes more intelligent and self-determined, possibly reaching a point where it becomes a person in its own right.

** ''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.

** 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?

** ''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 "{{Ubermensch}}" of genuinely superhuman ability.

* ''Literature/TheReluctantKing'': Gods gain strength from how much worship they receive. Those with the most are very powerful. Conversely, ones that have been deprived eventually fade into nothing.

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. A {{Tulpa}} is a creature that derives its existence from this force. Compare with WillingSuspensionOfDisbelief. See also AllMythsAreTrue, PsychoactivePowers, PuffOfLogic, and TheTreacheryOfImages. Might be a way of creating a DeityOfMortalCreation, or of justifying HolyBurnsEvil without implying that a given religion is objectively true in the setting (especially if holy objects from multiple mutually exclusive faiths are shown to repel evil).

* This is the core principle behind Christian Science. Diseases like cancer are an illusion and if you pray and believe in God enough you’ll be healed. Believers in this will sometimes refuse to be treated by doctors because of this belief -- this [[SurprisinglyRealisticOutcome generally doesn't end well for the believer]]. [[{{Music/Metallica}} James Hetfield]]'s mother was one such believer, and when she died after refusing to be treated for her cancer due to the belief that God would heal her, his anger about this would lead him to write [[ReligionRantSong "The God That Failed."]]

''(Monster is now fifty feet tall.)''

* Similar to the Doctor Thirteen example mentioned above, one power available to players in ''TabletopGame/{{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 of ''TabletopGame/{{GURPS}}'' 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 one of those cosmic ironies, the current powerset of ComicBook/CaptainBritain depends on his own confidence, much like Gladiator below -- the stronger his confidence, the stronger he becomes.

* In ''[[https://www.fanfiction.net/s/5136823/5/The-Life-of-Harry-Potter-and-Hermione-s-part-in-it The Life of Harry Potter and Hermione's Part in It]]'' a wizard's magic can become stronger through belief.

* According to Xander Harris in ''[[https://www.tthfanfic.org/Story-23251-11/BarefootXO+Time+and+Again.htm Time and Again]]'', belief is what makes vampires weak against holy objects rather than any innate power, making more popular religions such as Christianity, Islam, and Hinduism more effective. Furthermore, during the holiday season, a wreath on a door will prevent vampires from entering even public buildings or buildings they've been invited into because of the belief in Santa Claus by children all over the world.

* 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.

* ''WebOriginal/AbandonedByDisney'': The final story in the series [[spoiler:interprets Disney's entire "when you wish upon a star" imagery and their works in general to be a way to experiment with, and harness this. They're convinced that, when people believe in something intensely enough, and in big enough amounts, it may just come to be. Problem is, HumansAreFlawed, and negativity tends to seep into these attempts and corrode them, or even create them in their entirety out of terrible thoughts. This is why their every attempt has failed: Things do come into being through belief, but so far, all those things have been [[EldritchAbomination flawed, negative, and entirely wrong]]]].

* 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.]]

*** ''VideoGame/FateGrandOrder'': Carmilla can summon an IronMaiden to torture her opponents because people believe she used it to torture and kill people, even though it never actually existed. Music/WolfgangAmadeusMozart and Antonio Salieri were best friends, but Salieri's personality becomes twisted into hating Mozart because people think he was jealous of Mozart and murdered him. The Dioscuri Twins, Castor and Pollux, were gods, but their inaccurate legends turned Pollux into a demigod and Castor into a mortal, and they are ''pissed off'' about this. Romulus-Quirinus' father is Mars, but due to a legend that says his father was Hercules, he's able to use a version of Hercules' Nine Lives attack as if he was raised and taught by him, and he says the Servant Hercules feels like his father even though he still remembers Mars as his father.

*** This actually extends to when the normal people ''aren't'' directly observing a spell, too, the immediate impact just isn't as acute. Nature isn't actually natural, it's a carefully constructed useful lie that [[WellIntentionedExtremist the Technocracy]] taught to the mortals because of how everything being arbitrary and chaotic was hellish for most of humanity. For instance, there's not actually any such thing as gravity: you fall at 9.8 m/s2 near the earth's surface because that idea is engraved on the Sleeper unconscious by a wizard-run education system.

* ''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.

* ''TabletopGame/NewWorldOfDarkness'':
** ''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.
** ''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?
** [[SlasherMovie Slashers]] are human serial killers who often end up developing supernatural abilties. One type is the Legend: a killer who's stories have become so believed in that they find themselves gaining the abilities and weaknesses from those stories, even if they never had them before.
** ''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 "{{Ubermensch}}" of genuinely superhuman ability.
* In the ''TabletopGame/OldWorldOfDarkness'':

* The ''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 Your Hands 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.

** For one thing, [[GodsNeedPrayerBadly it applies to the gods and their power]]. If you look at sources that go into more detail about the background, like the TabletopRolePlayingGame resource ''TabletopGame/GURPSDiscworld'' or especially ''Literature/TheScienceOfDiscworld'' series, you'll see that the Discworld is set in a universe different from ours, with the powerful added combined element of [=magic/=]NarrativeCausality[=/=]power of belief. Narrative Causality especially ties to Clap Your Hands If You Believe and overlaps with it. On the Discworld, most people's beliefs about how the world works are as naïve and unrealistic and prone to forming neat narratives as in our world, but belief distorts reality so that they become sort of true in retrospect. So you might falsely believe your god is great and powerful, but when enough people believe the god is great, they ''will become'' powerful. Good luck trying to make the god good and wise, though -- that's not what you get by worshipping someone and giving them power. (Anyway, it's [[Literature/{{Pyramids}} been remarked]] that people don't really believe that's what their gods are like in the first place, even though of course they'll say that. Really what you expect is more like your father after a long day at work.)

* A rare inversion with the short story "Obstinate Uncle Otis" by the great horror writer [[http://scottnicolay.com/stories-from-the-borderland-4-4-the-believers-aka-do-you-believe-in-ghosts-by-robert-arthur-jr/ Robert A. Arthur, Jr.]] -- it's in ''Ghosts and More Ghosts'' -- 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 {{Your Mind Makes It Real}}ity. 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.

* In ''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 ''[[ArtisticLicenseBiology fully fertile offspring]]''.

[[folder:Films — Animation]]

* 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.

[[folder:Films — Live-Action]]

* Subverted in F. Paul Wilson's ''Literature/TheAdversaryCycle'' book ''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. In addition to this, changes in what people believe about a certain deity cause a new version of that deity to come into existance as an entirely seperate entity from the original.
* Laurel K. Hamilton's Literature/AnitaBlake novels: Religious symbols will only harm vampires if the person wielding it actually believes in it.
* 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 (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.

* In one book of the ''Literature/BloodWarTrilogy'' the protagonists have to hold off a demonic invasion in the Beastlands that will shortly arrive through a portal near a river. When one of the heroes asks a native what the river is called they respond by saying they haven't named it because it's holy to them leading to another of the heroes abruptly telling everyone to put up fortifications on the other shore without explaining why, later when the demon army shows up it turns out that the natives belief has [[HolyBurnsEvil turned the river into holy water.]]
* An early example: In Creator/AEVanVogt's ''Literature/BookOfPtath'' 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 ''Literature/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 dependance on belief was psychosomatic at first, but became this trope over time.

--> "Catch-22 did not exist, he was positive of that, but it made no difference. What did matter was that everyone thought it existed, and that was much worse..."
* In Creator/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 Your Hands 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.
* ''Literature/CruelIllusions'': The stage magicians' power is literally tied to the belief of their audiences. Their power is fed by the audiences believing that they can do their magic for real, and that gives the magicians a boost in power allowing them to do it for real.
* "Selecting Afterimages of the Fading", a short story by John Chu published in the anthology ''Defying Doomsday'', depicts a world where anything that is not sufficiently percieved eventually fades from existence. People known as "super-percievers" are regularly employed to keep things like farmland or buildings from fading, and most everything is a little blurry at least, but people can keep themselves workably intact with moderate self-attention. The protagonist is a high-capacity super-perciever, but his muscle dysmorphia keeps him from [[LogicalWeakness properly percieving himself]] so he needs help from others to keep from fading.
* 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. Tinker Bell's dead.
* This happens a lot in the ''Literature/{{Discworld}}'' series; for one thing, [[GodsNeedPrayerBadly it applies to the gods and their power]]. If you look at sources that go into more detail about the background, like the TabletopRolePlayingGame resource ''TabletopGame/GURPSDiscworld'' or especially ''Literature/TheScienceOfDiscworld'' series, you'll see that the Discworld is set in a universe different from ours, with the powerful added combined element of [=magic/=]NarrativeCausality[=/=]power of belief. Narrative Causality especially ties to Clap Your Hands If You Believe and overlaps with it. On the Discworld, most people's beliefs about how the world works are as naïve and unrealistic and prone to forming neat narratives as in our world, but belief distorts reality so that they become sort of true in retrospect. So you might falsely believe your god is great and powerful, but when enough people believe the god is great, they ''will become'' powerful. Good luck trying to make the god good and wise, though -- that's not what you get by worshipping someone and giving them power. (And anyway, it's [[Literature/{{Pyramids}} been remarked]] that people don't really believe that's what their gods are like in the first place, even though of course they'll say that. Really what you expect is more like your father after a long day at work.)

** The climax of ''Literature/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.]]

--->"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 universal trope for supernatural beings in ''Literature/TheDresdenFiles''. Magical beings don't necessarily require belief, but they DO require Knowledge of their existence in order to exist in the mortal world at all. Human perception can also shift their nature, sometimes even creating multiple distinct personalities for the same being. For example Odin is technically the same person as [[spoiler:Santa Claus]], although there are some differences. This has even been stated to be able to capable of cosmic scale Retcons. For example, if enough people believe that the Abrahamic God created the universe, then things will change such that God will have ALWAYS created the universe.

*** Interestingly, the above mentioned Knights of the Cross don't actually require Faith in {{God}}, with only one of them being particularly religious. Shiro was converted without understanding (but he tries his best to be a good Baptist regardless), Sanya is Agnostic (despite having received a magic sword from an archangel), and [[spoiler:Butters]], the most recent Knight of the Cross is [[spoiler:Jewish]] and not particularly religious. Uriel makes it clear that the important factor is faith in doing good and helping people in general, including defending others against evil as well as redeeming those who have made mistakes in the past. In Michael's case does this come along with his Christian Faith, but [[spoiler:Butters]] belief in ''Star Wars'' as a story of people fighting for good and triumphing over evil is a large part of his Faith, and Sanya simply seems to belive in doing good and helping people.
** 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 '''"I don't believe in faeries!!"''' It doesn't actually do anything , but certainly is good for the adrenaline. Knowledge of fairies does matter just like everything else, though, as Mab made sure the Brother Grimm published books of Fairy tales to ensure that humans continued to know about them. And on a smaller scale, the more authority Harry has give Toot-toot and the more he accomplishes, 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. [[GodsNeedPrayerBadly Him becoming the leader of the "'Za Lord's Guard" and gaining followers]] actually results in him personally becoming more powerful.
** 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 [[spoiler:Senior Council [=LaFortier=]]]'s murder involved no magic being slung. It is eventually revealed that the killer [[spoiler:was being mind-controlled]], but understood that they shouldn't be attacking [[spoiler:[=LaFortier=]]]. Meanwhile [[spoiler:[=LaFortier=]]] was too confused and shocked at the sight of someone they knew attacking them to magically defend themself.

** In the Novella ''Backup'', Thomas and Lara Raith are members of a secret society which uses this to banish creatures by making humans forget about them. The only way to truly win is to eliminate all knowledge of a particular being from humanity, 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 eliminate their competition. Word of God has discussed that this is also the purpose of [[spoiler:The Archive]]. Once everyone else has forgotten about a particular being, they wait for a few years, keeping an eye out for any mentions of the being until ultimately erasing their own memory of it as well, ensuring it is well and truly gone forever.
** This trope is conversed in Literature/SkinGame. Harry and a member of his crew come across the [[spoiler: real ShroudOfTurin]]. Someone asks why the fake has magic powers and Harry replies that if enough people believe the fake is real, it gains some power through belief. That being said, it's still pretty clear that the fake is not as powerful as the real deal.
* 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'' and ''Literature/TheTamuli'' 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.

* ''Series/DoctorWho'' Literature/PastDoctorAdventures;
** ''Salvation'' features a race of beings who gain power based on the belief others have in them, to the extent that they have been shaped into modern-day gods due to the prayers for salvation from the general population. Recognising the danger of these beings, at one point the First Doctor deliberately provokes the head of this pantheon into attacking him after inspiring doubt in the gods in their worshippers, with the result that he survives being hit by a fireball in front of a crowd of believers because his belief that he can’t be hurt outweighs the crowd’s belief in his attacker. The Doctor [[spoiler:later drives these beings away by dropping a dud bomb on the park where their congregation has gathered and making everyone present think it can hurt their ‘gods’]].
** In ''Deep Blue'', after determining that the nature of the Xaranthi infection is psychic, the Fifth Doctor is [[spoiler:able to use ordinary tap water and his own willpower to "convince" the Xaranthi that he has a cure for their transformation and force them to withdraw from Earth]].
* 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.
* In ''Literature/TheForbidden'' by Creator/CliveBarker, the original version of the ''Film/{{Candyman}}'' worked this way as much as his film counterpart. He needs people to believe in him to exist. Should someone doubt him or damage his reputation he will be obliged to show himself to them and take some innocent blood for good measure.
* In ''Literature/ForLoveOfEvil'', [[spoiler:Jehovah — the Jewish God]] says the number of believers in an Office determine the strength of the Office. Therefore, Satan's Office is extremely powerful because many people believe in Hell, but the powers of other deities wax and wane with the number of their believers.
* In the ''{{Literature/Freya}}'' series, this is the foundation of divinity. Belief defines all of the book's gods, physically and mentally, and this is discussed, played with, and even used - particularly by the villains - as a tool.

* [[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]].

* 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. The inverse also works: the scientist in the team doesn't believe in any of this and thus makes a fine AntiMagic weapon.
* 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/HellsKitchenSink'' The collective minds of humanity have formed entire pantheons. This is not the only source of magic, however.

* In the horror novel ''Literature/{{Jago}}'', a town is afflicted with a force that causes people's beliefs and obsessions to become real. A small boy is able to defeat the Evil Dwarf that lurks in his room after the lights go out by ceasing to believe in it; he finds that it's a lot less plausible when it appears in clearly visible physical form than it was as a vague possibility lurking in the dark. The manifestations that successfully do in the people who feared them tend to fade away afterward unless they've been witnessed by somebody else and a new belief created. The horrifically deformed revenant Badmouth Ben manages to survive for quite a while after taking his revenge on his murderer because he finds a NightmareFetishist who wants him to stick around. The manifestation of Danny Keough's terrors tries to get someone else to believe in her, but nobody else can because Danny's fears were so personal and idiosyncratic that nobody else can understand what she is, let alone believe that she exists.

* Creator/StephenKing:
** In ''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.
** This is a recurring theme for King, it shows up in ''Literature/NeedfulThings'', the Sheriff is able to assault the demonic Gaunt with a bunch of sleight of hand tricks made into real sorcery by simply willing himself to believe it'll work. Conversely in ''Literature/TheStand'', sociology professor Glen Bateman understands the nature of Flagg's powers and is so focused on believing that Flagg's magic only works if one believes in it, that Flagg really couldn't cast anything on Bateman and had to order a lackey to shoot him. A little later against a rebellious cultist, Flagg is able to roast him alive with magic because of the man's fear and belief.
** Taken to it's most ridiculus degree in ''The Library Policeman'' where the hero attacks the villan with a ball of red vine licorice. Because the licorice has a special significence to him, it works.

* 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. It's also noted that most theologians consider the whole thing "a load of Dingo's kidneys".

* 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]].

* A rare inversion with the short story "Obstinate Uncle Otis" by the great horror writer [[http://scottnicolay.com/stories-from-the-borderland-4-4-the-believers-aka-do-you-believe-in-ghosts-by-robert-arthur-jr/ Robert A. Arthur, Jr.]] -- it's in ''Ghosts and More Ghosts'' -- 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 {{Your Mind Makes It Real}}ity. 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.

* The mythical Tlön culture in "Literature/TlonUqbarOrbisTertius" is capable of this; they don't believe in a mind-independent reality, so reality becomes dependent on their minds.
* 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.)
** On the play's opening night, Nina Boucicault as Peter cried out ''"Clap your hands!"'' and the applause was so immediate and overwhelming that she burst into tears.

* 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.
* Mundanes are largely immune to being attacked by maleficaria in ''Literature/TheScholomance'' books by Naomi Novik, because if they spot them at all, they don't believe they're seeing a dangerous magical beast, and the mal loses both its magic and its danger. El's gym teacher once spotted a creature that was trying to get the jump on El, thought it was a rat, and killed it with a cricket bat. El, who is prophesied to destroy wizard society with her apocalyptic magic, says that she could not kill even a small mal with a piece of wood.

* 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 ''[[ArtisticLicenseBiology fully fertile offspring]]''.

* 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.
* ''Literature/SummerOfNight'': This is vaguely and strangely alluded to when one of the BigBad's minions explains that it is [[HolyBurnsEvil vulnerable to holy water]] due to a habit acquired from hanging around in the Vatican in the past. Of course, this leaves the details very unclear. Is it about the monster's unwilling Catholic beliefs? Is it just an excuse and the holiness itself really has an effect?
* In ''Literature/DadAreYouTheToothFairy'', fairies apparently [[HereThereWereDragons existed centuries ago]] but then had to leave "[[ScienceVersusMagic because of technology]]" and can still communicate with children's parents, but only if the kid believes in them.
* ''Literature/TheReluctantKing'': Gods gain strength from how much worship they receive. Those with the most are very powerful. Conversely, ones that have been deprived eventually fade into nothing.
* ''Literature/WildCards'': Characters theorize that the Wild Card virus works this way, causing the acquired powers to follow rules that their owners believe in. Unfortunately, the characters are not generally capable of consciously controlling their own beliefs, so trying to use this information to alter one's powers risks unpredictable results.
%%* Norman Vincent Peale's ''The Power of Positive Thinking'' is all about this.
* ''Celestial Wars'':
** While celestials have certain innate powers, if a mortal believes in them they also gain whatever additional powers the mortal thinks they have (i.e. If a celestial's worshippers believe he has the power to control the weather, he can control the weather. If the worshippers believe the celestial can raise the dead, she can raise the dead). This is referred to as the "powerbase".
** The powerbase is counterbalanced by the "thrall": a celestial also gains whatever flaws, vulnerabilities, and beliefs her worshippers think she has. Hephaestus's worshippers believe that he is crippled after being thrown off Mount Olympus, and so he is crippled. The Norse pantheon's worshippers believe that they will die if they don't get Idun's apples once a year, and so it becomes true. If a god's followers were convinced that he was a womanizing asshole, he would become a womanizing asshole.
** In addition, an established celestial is immutably convinced that their current powerbase and thrall is right and proper and the way things should be, and will fight tooth and nail to preserve it, even if it is objectively horrible.
** For a further complication, unless a celestial is attuned to the realm they are in (a process that can take centuries), then he must be within fifteen feet of a mortal for the mortal's belief to have any effect. If attuned, the worshipper need only be in the same realm. In case of contradictory beliefs, the belief with the most backers becomes true.
** And as one final twist, a celestial cannot permanently die (by any means) so long as they have an active powerbase somewhere, even if they are currently out of range of that powerbase.
* ''Literature/TheBrokenEmpireTrilogy'' takes place in what seems to be a horrific fantasy world with magic and undead monsters, but is actually a [[AfterTheEnd post-apoctalypstic hellscape]] brought on by the "Builders" (us) messing with quantum physics and ripping he fabric of reality. The result is that, because people believe in things like heaven, hell, angels, demons, the undead, and magic, all of those things exist, feeding off people's expectations. This also holds true for the sequel series, ''Literature/TheRedQueensWar''.
* ''Literature/NecroticApocalypse'': Even though they can't make use of it consciously, all living things naturally have a mana system, and can sometimes unconsciously create powerful magical effects when enough people believe something strongly enough. This has been going on for all of human history, but these effects are universally either subtle or completely irrelevant to daily life. Churches have a sanctuary effect that changes the local mana balance and keeps certain monsters out, but since no one can access their mana and monsters didn't exist until recently, no one noticed. Digby loots the Cloak of the Goblin King from a display for ''Film/{{Labyrinth}}'' and finds that it provides a passive mana buff, which again is irrelevant to anyone who doesn't have their mana enhanced already.
* Discussed in ''Literature/JohnDiesAtTheEnd''. The various monsters/demons are repelled by holy symbols like crosses, and Dave wonders at one point if this is because the people wielding the symbols believe that should happen, or because ''the monsters'' do, or because [[MaybeMagicMaybeMundane the symbols simply are genuinely divine]].
* ''Literature/{{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 is once confronted by Dynast Graushera's General, a very powerful Mazoku. Realizing she can't fight or escape, Lina decides to try mocking the Mazoku's name. The reasoning is that because Mazoku are masses of astral energy held together by their own self image, anything that undermined their self confidence will make them weaker. The strategy works.
* In ''Literature/AmagiBrilliantPark'', the fairies from Maple Land need people to like and believe in them or else they will cease to exist. After settling down on Earth, they opened up a theme park with them as the star attractions. The story starts with the park declining in popularity and threatened with foreclosure, so they bring in intelligent human Seiya Kanie to bring the park back in shape and save them. They comment that some of them could probably survive by turning into begging street performers, but that isn't really an option for the less talented and less attractive among them.
* ''Literature/ACertainMagicalIndex'':
** 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.
** WordOfGod is that Level 5 (the highest level) espers are as powerful as they are simply because it never occurred to them that they would be anything else.
** A mysterious entity seems to be the legendary figure St Germain. It is eventually revealed that St Germain never actually existed in this universe, but this entity was manifested to play the part due to a lot of people believing in his story.
* ''Literature/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.
* ''Literature/TheMisfitOfDemonKingAcademy'':
** Spirits essentially exist due to this, as they are based on the rumors, myths, legends and traditions that people believe in. For instance, a strong fear of fire will create fire spirits while if people have faith in water, water spirits will be produced. Spirits can even survive having their source destroyed as long as enough people maintain a belief in their tradition. However, spirits are highly dependent of their tradition and if that fades, the spirit will cease to exist and if there are traditions that contradicts each other in regards to a particular spirit, their lifespan will be shortened. In addition, if a spirit itself deviates for its established lore, their source will be crushed and they will die.
** The most interesting case would be [[spoiler:Misa Ilioroagu, who is a half-demon/half-spirit, and the biological daughter of Reno, the mother of all spirits. As the TopGod; Nousgalia, wanted to create a being to destroy Anos Voldigoad; The Demon King of Tyranny, who constantly opposed the gods, he set about to use Misa as a tool to do so. By taking advantage of Hero Kanon's FalseFlagOperation to save Anos by creating a fictional Demon King to be TheScapegoat for human hate, Nousgalia exploited the plan by syncing Misa's source to the tradition of Avos Dilhevia, the fictional Demon King, thus giving her power equal to that of Anos and the ability to usurp control over anything that was associated in tradition with the Demon King of Tyranny, such as his subordinates; Seven Elder Demon Emperors and his castle; Delsgade.]]

* In the ''Series/BuffyTheVampireSlayer'' episode "[[{{Recap/BuffyTheVampireSlayerS1E11OutOfMindOutOfSight}} Out Of Mind, Out Of Sight]]", 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).

* ''Series/TheColbertReport'': 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.

** In [[Recap/DoctorWhoS26E3TheCurseOfFenric "The Curse of Fenric"]], a cross works on [[OurVampiresAreDifferent Haemovores]] only if the bearer has faith in it, and other objects of faith work equally well: a WWII Soviet soldier fends them off with a red star cap badge, and the Doctor is able to hold them at bay with no physical object, simply by invoking his faith in his companions. The priest who doubts his faith meets a sticky end.
** [[Recap/DoctorWhoS29E13LastOfTheTimeLords "Last of the Time Lords"]] 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 Tinker Bell [[CrystalDragonJesus Jesus]] or Fairy Doctor.
** [[Recap/DoctorWhoS31E13TheBigBang "The Big Bang"]]: [[spoiler:The Doctor was erased from existence, but Amy remembers him and somehow magically brings him back.]] It... ''sort of'' [[ItMakesSenseInContext makes sense in context]].
** The Doctor [[Recap/DoctorWhoS32E4TheDoctorsWife 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.
* ''Series/ForeverKnight''. In one episode a woman whom Nick Knight had dismissed as being a vampire because she'd been seen in daylight turns out to have a SplitPersonality, one of which was vampire and the other human. Dr. Natalie Lambert sees this as a good sign, and in an AmnesiaEpisode she's hopeful that if he doesn't remember he's a vampire he'll be cured, but it doesn't work out that way; he can eat solid food but is still scalded by sunlight and she has to tell him the truth.
* In ''Series/{{Good Omens|2019}}'', when London is surrounded by a ring of hellfire along the M25, Crowley decides to drive right through it. [[spoiler:Hastur is burned to ash almost instantly]], but Crowley just keeps on driving, and the car manages to survive without melting to burst out of the wall of fire on the other side. Crowley just keeps telling the car that it can handle it. God's voiceover explains that, unlike every other demon, Crowley has developed an imagination over the 6000 years of living on Earth. So, as long as he's convinced that neither his body nor the car have been burned to a crisp by the hellfire, that is indeed what's happening. Plus, [[spoiler:he's hurrying to save the world and, most importantly, his best friend, the angel Aziraphale]].
* On one episode of ''Series/{{Haven}}'', this trope mixes with YourMindMakesItReal when a ConspiracyTheorist who believes in aliens causes AlienInvasion signs (i.e. CropCircles, abductions, UFO sightings) to occur throughout the town.

-->'''Gai''': I don't really understand, but...when I imagined it, it came true! The first debut of this historic form! Go-on Silver and Go-on Gold! These two are a single Go-on Wings!

* On BBC ''Series/Merlin2008'', 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 Tinker Bell and making everyone clap for her.

* ''Series/{{Quark}}''. Parodied in "May The Source Be With You". To stop a Gorgon invasion, Quark is trusted with the Source, which can make anything possible as long as you believe in it. But as it's such a powerful weapon, the Source has been sealed up for 200 years and is now suffering from confidence issues.
* It turns out this is the case in ''Series/ResshaSentaiToQger'' [[spoiler:where the Toqgers are children, given adult bodies to able to get the best of both worlds when fighting the Shadow Line: Able to handle the darkness better and able to handle combat better of a adult while still possessing strong imagination of a child. This becomes somewhat of a minor plot point as it commented that if the Toqgers are continuously exposed to darkness the chances of being able to be successfully returned to their true ages will decrease.]]
* ''Series/{{The Sandman|2022}}'', "[[Recap/TheSandman2022S01E11ADreamOfAThousandCatsCalliope A Dream of a Thousand Cats]]": The Prophet's message is that the nature of reality can be changed more easily than people realize -- if enough people, perhaps as few as a thousand, all dream the same thing at once, that will become reality. It's already happened once, creating the damaged and strife-torn world we inhabit, and the Prophet is trying to gather believers to make it happen again and create a better world (that is, one that's better for the Prophet and her followers).

** A season 2 sketch features John Beliushi as Tinker-Bee, who not only demands the audience clap to save him from dying...but also a standing ovation!

* 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.

* 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 [[GodsNeedPrayerBadly a lack of followers]].
** The Franchise/StarTrekExpandedUniverse has "the Beings" in Peter David's ''Literature/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 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 as it had been posted online. The Winchesters were eventually able to stop it by creating a myth of its weakness, but Sam was left 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.

* One episode of ''Series/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".

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* ''Theatre/{{Peter Pan|1904}}'': The TropeNamer, dating [[OlderThanTheyThink all the way back to the 1904 stageplay]]. Tinker Bell [[TakingTheBullet intentionally drinks a poison]] meant for Peter, and Peter [[BreakingTheFourthWall appeals to children everywhere]] to [[InvokedTrope invoke this trope.]] Naturally, this was an AudienceParticipation bit.