->''"The very powerful and the very stupid have one thing in common. They don't alter their views to fit the facts, they alter the facts to fit their views."''
-->-- '''The Doctor''', "[[Recap/DoctorWhoS14E4TheFaceOfEvil The Face of Evil]]"

Everyone has their own view on the world and what happens around them. Maybe Bob believes that HumansAreBastards. Maybe Alice thinks Chris is going to betray her. Given enough time, though, these views and opinions can change, allowing Bob to see the good in man, and Alice to start to trust Chris. This trope is when that never happens; A character suffering from Theory Tunnel Vision will stick with whatever idea he or she has for way longer than what would be normal. Even if Bob meets hundreds of {{Good Samaritan}}s, he'll keep stating that HumansAreBastards, and Alice will never trust Chris even though he saved her life several times now.

There are several kinds of Theory Tunnel Vision, and several reasons for someone suffering of it:
* Pride/stubbornness: Bob is just too proud or stubborn to say that he's been wrong, instead keeping up his own version of reality.
* Familiarity/indoctrination/Prejudice: Bob has been told every day of his life that group X is evil. As a result, nothing group X will ever do can change Bob's vision. Even if someone from group X would rescue Bob from a burning building, all he'd say is to let go of him.
* Hostility: Bob has a certain view of the world. Alice, his nemesis, states that he is wrong and has a lot of evidence to support her. However, since Alice is Bob's nemesis, he has no reason to believe her, even if the evidence is groundbreaking.
* Trust: Bob simply cannot believe that Alice would ever do something bad; even when she steals money right out of his hands, he deems it an accident. This one pops up very often with parents towards their children.
** Broken Trust: Bob has been betrayed so many times in his life that he simply cannot believe that someone would ever do something good. Even if Alice helps him pay his monthly bills, he sees it as a way to get him in debt with her.
* Mental disorder: Due to a handicap, Bob believes that whatever he thinks is true, is in fact true; anyone who states otherwise is deemed a liar.

Theory Tunnel Vison can be both positive and negative, and the person suffering from it can be proven right in the end. The key point is that someone who suffers from it will [[SelectiveObliviousness discard any and all evidence]] that proves him or her wrong, no matter how solid it is.

If someone suffering from Theory Tunnel Vision at some point ''does'' break, expect a HeroicBSOD, along with muttering about how this should be impossible. A fair warning, though: Do not try to break Theory Tunnel Vision on purpose, as there is a good chance that you'll lose your friendship with the sufferer... or worse.

SelectiveObliviousness is the supertrope of this; FlatEarthAtheist and TheScully are subtropes. A staple technique of the TautologicalTemplar. TheFundamentalist is the logical extreme of this, building everything around a few notions held this way. What develops into Theory Tunnel Vision may start out as AggressiveCategorism.

TruthInTelevision; even normal, non-neurotic people will take considerable evidence to overwhelm a strongly-held theory, let alone those in psychological denial who'll get angry at people pointing out reality.

!! Examples:


[[folder: Anime and Manga ]]

* In ''Anime/{{Monster}}'', detective Lunge initially believes protagonist Dr. Kenzo Tenma to be the serial killer. Over the course of the series, evidence that Johan is the real killer is practically thrown at him, from close acquaintances of Johan to criminal psychiatrists. However, Lunge continues to believe that Johan is a pseudonym for Tenma. It isn't until [[spoiler:near the very end, when Lunge sees Johan with his own two eyes, that he realizes Johan is a real person]].
* In ''LightNovel/GroundControlToPsychoelectricGirl'', Erio was in a tragic accident wherein she went missing for three months and then turned up on a beach without any memory of the intervening time. Her reaction was so bad that she invented a story that she had been abducted by aliens and convinced herself that was the only explanation. After a few months, she tried to test her theory... only be injured ''again''. But again, because she was far too fragile to face reality, she only drew even further into her fantasy world, to the point of becoming a {{Hikikomori}}. Later, her cousin forcibly proves to her that she isn't an alien, but after an initial highly negative reaction, she seems oddly okay and is even willing to regain society again.
* In ''Anime/KillLaKill'' Ryuko comes to believe that StudentCouncilPresident Satsuki Kiryuin was responsible for her father's death before the start of the series, since Satsuki claims to have knowledge about why it happened. She becomes so fixated on this that her flashbacks when she barely saw the killer fleeing the scene start to shift so the figure resembles Satsuki, meaning that when [[spoiler:the ''real'' killer reveals herself it comes as quite a shock to her.]]


[[folder: Live Action TV ]]

* In the ''Series/{{Buffy the Vampire Slayer}}'' episode "I Only Have Eyes For You," Giles is convinced that a haunting is [[spoiler:Jenny]] trying to communicate, despite all evidence to the contrary.
* ''Series/{{Dexter}}'': Multiple times throughout the show, a character will suspect something is off (to the point of a CassandraTruth) and Dexter will have to invent evidence to turn them away. It often works. One extreme example when it doesn't is when Laguerta adamantly believes that Doakes is innocent and no matter what evidence Dexter plants to the contrary, she still stands by this belief.
* In ''Series/{{Monk}}'', there was an episode with a nudist. Adrian's theories got crazier and crazier as he tried to explain how the nudist was guilty.
* A regular feature of ''Series/DoctorWho''. The Doctor arrives in a situation, announces that what's going on is nothing like what the local authority figure believes, and is immediately worked into the authority figure's theory as being part of the problem. However, the Doctor has been known to suffer from tunnel vision himself, for instance in "The Monster of Peladon", where he finds it hard to believe the Ice Warriors aren't the baddies.


[[folder: Literature ]]

* In ''Literature/HarryPotter'', the eponymous character is dead set on blaming anything and everything that goes wrong at Hogwarts on Snape or Malfoy.
** In ''[[Literature/HarryPotterAndTheHalfBloodPrince The Half-Blood Prince]]'', Harry is convinced that Draco has become a Death Eater and is up to some evil scheme. Even after compelling evidence is offered showing Draco wasn't even around when a certain event occurs, Harry refuses to consider the possibility that Draco wasn't involved. In a case of RightForTheWrongReasons; Draco actually ''was'' up to something, and was involved in several of the mysterious events, but Harry was drawing his conclusions from gut instinct and his personal hatred for Draco rather than any actual evidence. It's also a case of DramaticIrony, as a chapter at the start of the book proves to the readers that Voldemort has set Draco some unspecified task, but none of the good guys knew about it.
* In ''TheLastBattle'', Dwarves are in paradise eating a feast, but they believe they are in a hut eating slops. This does at least have a mystical explanation, as it is caused by Aslan's power, and is part of Lewis' AuthorTract on how atheists could have God and Heaven right in front of them but be unable to see it.
* Something of a recurring theme with guards in [[ForgottenRealms Ed Greenwood]]'s novels, who seem to be prone to theorizing that ''anyone at all'' they don't personally know and who wants to get past them is up to no good and therefore needs to be brushed off, arrested, or simply killed outright. A classic example in the "Shadow of the Avatar" trilogy has the protagonists come back from a patrol for the Lord of Shadowdale and be accosted by guards ''of'' the Lord of Shadowdale, who casually dismiss all their claims and seem all too eager to engage in some casual bloodshed for their own amusement (to be fair, those particular guards were newly hired, but still).


[[folder: Tabletop Games ]]

* ''TabletopGame/{{Warhammer 40000}}'': Part and parcel of the CrapsackWorld nature of the setting, since the Imperium runs on fundamentalism and rigid discipline. One reason Ork kommandoes (seven foot tall killing machines who are stealthy and able to perform covert missions in addition to being the charge-happy dakka-shooting lunatics we know and love) are successful is that a Guardsman who tried to report their existence was executed for cowardice as what he said went against Imperial doctrine.


[[folder: Video Games ]]

* In ''VideoGame/SuperPaperMario'', upon hearing that Mushroom Castle was attacked and Princess Peach was kidnapped (AGAIN!), Luigi immediately decides that Bowser must've been behind it.
* Played for laughs in the ''Hordes of the Underdark'' expansion for ''VideoGame/NeverwinterNights'' -- if you have Deekin with you in Hell, he interprets the signs of battle between Demons and Devils as the remnants of something long and complicated involving dragons.
* Walker in ''VideoGame/SpecOpsTheLine'' is always certain that he's doing the right thing and that the 33rd are in the wrong, despite the mounting evidence to the contrary. He finally recognizes the truth at the end of the game.


[[folder: Web Comics ]]

* In ''Webcomic/SchlockMercenary'', during the Mahuilotu arc, the local police just cannot get over the idea that the [[EverythingsEvenWorseWithSharks killer shark]] was some kind of "murder-sub" built by John der Trihs. (They knew that their terraformed planet didn't have any sharks. Why blame John? They probably figured that he who smelt it dealt it.)
** The Toughs later threaten to sue the idiots for what their lawyer calls "impersonating a police force".
* In ''Webcomic/{{Homestuck}}'', Terezi finds the corpse of [[spoiler:Tavros]] and immediately concludes that Vriska is the most likely suspect. As she searches the crime scene for clues, Terezi admits to herself that she's only pretending to not already know who the murderer was. Then she finds the bodies of [[spoiler:Feferi and Nepeta]] and concludes that Vriska's on some kind of killing spree. She's a bit taken aback when Vriska freely admits to killing [[spoiler:Tavros]], but isn't even aware that the others died.
** Note, that while [[spoiler: Gamzee]] had staged the last crime scene to frame Vriska, it was only after they found out about Terezi's personal conviction, and [[spoiler: John]] later remarks on how poorly staged said scene was.
* ''Webcomic/ElGoonishShive'' got those two [[http://www.egscomics.com/?date=2010-04-16 alien]] [[http://www.egscomics.com/?date=2010-12-27 enthusiast]] [[http://www.egscomics.com/?date=2011-06-20 nerds]] annoying people. Hilariously enough, they never noticed real aliens and half-aliens in their town.
* ''Webcomic/TheOrderOfTheStick''
** Tsukiko firmly believes that HumansAreBastards, and as the opposite of the living, undead are good underneath everything, despite the total lack of evidence for this. She starts to realize she may be wrong as [[spoiler:her wights are controlled into draining her to death.]]
** Miko is unable to comprehend that anyone who is good might disagree with her methodology, therefore the Order (who defend Belkar, who is evil) are also evil. Her determination to stick to this belief in the face of all the evidence eventually leads her to full-blown paranoia [[spoiler: and fall from paladinhood when she concludes that her sworn lord, since he "conspired" with the Order, is also evil ... and betrays her oath by killing him. This, of course, she interprets as further evidence of the Order's evil; they "tricked" her into abandoning her vows.]]


[[folder: Web Original ]]

* In ''ThereWillBeBrawl'', Mario immediately assumes Bowser is behind Peach's latest kidnapping, and refuses to hear any other explanation... not that you could blame him, of course. He only relents when [[spoiler:Luigi tells him of Bowser's death]].