Everyone has their own view on the world and what happens around them. Maybe Bob believes that Humans Are Bastards. 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 Samaritans, he'll keep stating that Humans Are Bastards, 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 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 Heroic BSoD, 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.
Selective Obliviousness is the supertrope of this; Flat-Earth Atheist and The Scully are subtropes. A staple technique of the Tautological Templar. The Fundamentalist 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 Aggressive Categorism.
Truth in Television; 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.
- In 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 near the very end, when Lunge sees Johan with his own two eyes, that he realizes Johan is a real person.
- In Ground Control to Psychoelectric Girl, 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 Kill la Kill, Ryuko comes to believe that Student Council President 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 from when she barely saw the killer fleeing the scene start to shift so the figure resembles Satsuki, meaning that when the real killer, Nui Harime, whose Mega Twintails make her a dead ringer for the initial silhouette, reveals herself, it comes as quite a shock to her.
- Played for tragedy in Your Lie in April. Early on, it is shown that Kousei's late mother Saki once beat him bloody for underperforming at piano, causing him to wish she was dead. Later, we see the same event from her point of view, where she confesses to a close friend that she pushed him to abusive extents because she was terminally ill and convinced that piano mastery was the only way he could make a living after her passing. Whether this puts a sympathetic sheen on a secretly-broken woman's tough love or just makes her more monstrous for being blind to any other ways Kousei could have gotten by remains one of the divisions in the fandom.
- Doctor Doom simply cannot get it out of his head that Reed Richards was responsible for the accident that disfigured him. Being something of an egomaniac, he naturally assumes Richards thinks like him, and occasionally designs traps that would be impossible for Doom to escape... and that Richards just strolls out of.
- Lex Luthor once discovered evidence that Clark Kent is Superman... and promptly dismissed it, because why would a Physical God use such a humble personality? A lot of his rage can be put down to Superman not acting the way Luthor would act with all that power, and it drives Luthor nuts.
- Hugo Strange projects his many, many neuroses onto Batman, certain that he only fights crime because he gets off on beating weaker people (Strange being a short, glasses-wearing psychiatrist who occasionally dresses as Batman).
- J. Jonah Jameson is convinced that Spider-Man is a threat and a menace, and no matter how many acts of heroism Spider-Man performs, nothing will change his mind.
- RainbowDoubleDash's Lunaverse: The Element Bearers are utterly incapable of seeing Corona (also known as Celestia) as anything but an arrogant, cruel, greedy monster who'd kill them all given half a chance. This backfires when they're forced to work together, and the six of them think backstabbing the Physical God who's agreed to work with them is a better idea than stopping the necromancer who's trying to become immortal. In fairness, though, they're part of a culture that's been fed a thousand years worth of stories about how evil she is, and when they first met, she kidnapped some of their loved ones, on account of being completely insane. But even after she's cooled down somewhat, they still refuse to think she's not pure evil.
- Flat out lampshaded in Girl Days where Kunou, Ryouga and Mousse are all mentioned to "take the facts and jam them into their viewpoint."
Author's Note: The astute reader will notice that Ryouga Hibiki has what can be best described as an unusual logic system. Rather than going from facts to conclusion, one starts at the conclusion and jams the facts around it. And in the minds of the likes of Ryouga Hibiki and Tatewaki Kunou, we all KNOW what the conclusion is.
- The Caine Mutiny: This is ultimately what exposes Captain Queegs mental issues; after a quart of strawberries goes missing from the ships galley, Queeg becomes convinced that theres some sort of dangerous and recurring food theft going on, concocting an elaborate vision of the heist. He soon forces the crew to practically turn the ship upside down in search of a duplicate key that exists only in his imagination and outright when hes directly told what really happened (a couple of mess boys ate the strawberries as a snack), he outright ignores it and continues his investigation. He ends up damning himself in the court when he goes on a paranoid rant about the strawberries while on the stand, undoing all of the prosecutions work and making it clear that Queeg truly wasnt in a fit state of mind.
- A woman suspects her husband is cheating on her. She takes advice from her friends, who tell her to look for Affair Hair. When her husband comes home and she can't find any, she's horrified and disgusted — her husband is cheating on her with a bald woman!
- The Chronicles of Narnia: In The Last Battle, 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' Author Tract on how atheists could have God and Heaven right in front of them but be unable to see it.
- Forgotten Realms: Something of a recurring theme with guards in 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).
- In Harry Potter, the eponymous character is dead set on blaming anything and everything that goes wrong at Hogwarts on Snape or Malfoy. In 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 Right for the Wrong Reasons, 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 Dramatic Irony, 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.
- Sherlock Holmes believes guesswork leads to this, refusing to discuss a case before he has all available data. He often has multiple theories before finding that out, going on what the newspapers say, but these are inevitably discarded before the end.
- In the Buffy the Vampire Slayer episode "I Only Have Eyes For You," Giles is convinced that a haunting is Jenny trying to communicate, despite all evidence to the contrary.
- Dexter: Multiple times throughout the show, a character will suspect something is off (to the point of a Cassandra Truth) 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 no matter what evidence Dexter plants to the contrary, she still stands by this belief.
- A regular feature of Doctor Who.
- 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 themself, for instance in "The Curse of Peladon", where the Third Doctor finds it hard to believe the Ice Warriors aren't the baddies.
- The Twelfth Doctor, who despises war and killing and hates himself for hurting innocent people, cannot believe that Clara's ex-soldier boyfriend Mr. Pink is anything but a Blood Knight who glories in death and destruction. Mr. Pink, now a middle-school teacher who also despises war and killing and hates himself for hurting innocent people, upon learning the Doctor is a Time Lord, cannot believe that an officer ("an aristocrat!" at that) is anything but an Upper-Class Twit Glory Hound who doesn't care about "lower people" getting hurt. In the end, they agree that Clara loves them both and that's all that really matters. (The Doctor also settles on referring to Pink as a muscle-headed PE teacher [Pink teaches math], which is probably an upgrade from heartless killer soldier.)
- In 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.
- Warhammer 40,000: Part and parcel of the Crapsack World 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.
- Paranoia: After the Big Whoops, when The Computer was trying to figure out what the hell to do next, the first usable files it found were civil defense files from 1957. It promptly decided that Alpha Complex was being invaded by the Commies, and rejected all evidence to the contrary as an elaborate Commie plot to obscure the truth.
- In Super Paper Mario, 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 Neverwinter Nights — 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 Spec Ops: The Line 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.
- The Batman: Arkham Series version of Riddler is so convinced that Batman is nothing more than a thug that bullies those weaker than him and that his tech is stolen than others, that after Scarecrow removes Batman's mask in live television, Nigma refuses to believe it and "figures out" that the entire thing was a conspiracy created by Batman, Scarecrow, and most of the human populace just to trick him.
- In Schlock Mercenary, during the Mahuilotu arc, the local police just cannot get over the idea that the 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 Homestuck, Terezi finds the corpse of 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 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 Tavros, but isn't even aware that the others died.
- Note that while Gamzee had staged the last crime scene to frame Vriska, it was only after they found out about Terezi's personal conviction, and John later remarks on how poorly staged said scene was.
- El Goonish Shive has got those two alien enthusiast nerds annoying people. Hilariously enough, they never noticed real aliens and half-aliens in their town.
- The Order of the Stick
- Tsukiko firmly believes that Humans Are Bastards, 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 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 and falling 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.
- Redcloak believes O-Chul is hiding information about the defenses of Girard's Gate from him despite multiple torture sessions and every coercive spell he can think of. The fact that O-Chul doesn't know (the first five guardians of the Gates swore not to look for the gates' locations precisely in case this happened) isn't about to stop him. In Redcloak's case, it's actually a subversion: while he is baffled that the Sapphire Guard would throw away the security of the world for a foolish promise by their predecessors, he's accepted it and is using the interrogation as an excuse to hang around Azure City instead of continuing to the next Gate as per Xykon's intentions.
Redcloak: I find it far more probable that you are somehow resisting my magic. This "Soon's Oath" story is just that — a cover story designed by your leaders. [...]
O'chul: You find the idea that I have some sort of secret knowledge implanted in my brain by the elders of the Sapphire Guard that has been so deeply suppressed that no magical effect can unearth it to be simpler... than the idea that I just don't know anything?
Redcloak: I like the way I phrased it better.
O'chul: No doubt.
- In There Will Be Brawl, 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 Luigi tells him of Bowser's death.
- Denzel Crocker in The Fairly OddParents! immediately attributes anything slightly unusual to fairy godparents. Granted he is correct a lot of the time, but he is just as quick to attribute completely mundane events to them.
- Shredder in Teenage Mutant Ninja Turtles (2012). He claims Splinter is responsible for everything bad in his life. At first it seems like he's just lying to manipulate his henchmen, but soon it becomes clear that he seriously believes in the bizarre conspiracies he attributes to Splinter, violently rebuking any evidence to the contrary. He clings to this theory so obsessively that he sometimes seems to be outright delusional; at one point he sincerely claims to have watched Splinter murder somebody that he himself killed.