"To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy, to forget whatever it was necessary to forget, then to draw it back into memory again at the moment when it was needed, and then promptly to forget it again: and above all, to apply the same process to the process itself. That was the ultimate subtlety: consciously to induce unconsciousness, and then, once again, to become unconscious of the act of hypnosis you had just performed. Even to understand the word 'doublethink' involved the use of doublethink."The ability to simultaneously believe in at least two or more mutually contradictory concepts, without any cognitive dissonance. You do know better and what's really true, but you still keep Believing Your Own Lies as the truth just because. There are two kinds of straight examples here: Verified examples, where a reliable narrator or similar gives the audience insight into the mind of the character, and apparent examples where a character appears to be engaging in doublethink but we don't know for sure what's really going on in his mind. Examples of the latter kind are more effective when a character suspects another of doublethink. Hypocrites often engage in doublethink, though the Straw Hypocrite doesn't have to, being dishonest to others rather than themselves. In cases where doublethink is combined with some version of The Masquerade, it becomes an extremely potent tool of the Consummate Liar: No liar is as believable as the honest liar who truly believes in his own lies. Compare and contrast No, Except Yes and From a Certain Point of View, where a character tries to glue opposing viewpoints together as being the same thing, giving it a resemblance of coherence by various esoteric distinctions. Compare Memory Gambit & Poe's Law. Contrast Becoming the Mask, where cognitive dissonance sets in and a character who has pretended to be loyal to a certain group starts gaining true loyalty towards it, and Both Sides Have a Point where both sides are respected but kept separated. See also 2 + Torture = 5 and The Treachery of Images.
- The entire Sucker Punch story runs on this, as the character(s) live simultaneously in two or sometimes even three different levels of realities, requiring quite a bit of multitasking from the audience if they are to have any real clue as to what's going on. At the end it is revealed that Baby Doll did manage to help Sweet Pea to escape in the real world. This means that she must have been active in all three realities simultaneously, and actually accomplishing real deeds while trapped within a dream within a show within a hallucination. Wow.
- George Orwell's 1984 is the Trope Namer. The party requires that all citizens believe everything that the party says, even when they know for a fact that it is not true. Ingrained in this concept is also the idea that Your Mind Makes It Real. If everyone believes that something is true, then it is true. Thus, the party can literally dictate reality.
- Dios and the other Djelibeybian priests from Pyramids are noted for this ability, as religious dogma in that country obliges them to believe that several different gods all exclusively and simultaneously fill the same divine offices. Most of the priests are dedicated to one god (not dismissing the existence of the others, but at least not having to think about their interaction too much), but as high priest Dios believes in all of them.
- Vorbis from Small Gods has mastered doublethink to the levels applied by the Party, as he's quite comfortable declaring that the way things may actually be found to be in the world is insignificant compared to the fundamental truth. For example, if you could actually go to the edge of the world and see that it is a disc (which you can, in this case), that doesn't matter because the real truth still is and always will be the dogma that the world is round, though of course anyone claiming it's a disc must be silenced before they corrupt the minds of believers.
- In order to use sympathy in The Kingkiller Chronicle, one must be able to hold two opposite beliefs at once. It sounds simple at first, but it's also one of the reasons most Arcanists go mad.
- In Blå Tornet, the protagonist survives through his youth by developing this mindset. He is truly a heretic, but he is also a priest in a society hellbent on sniffing out all heretics and burying them alive. His solution is to never lie, a lie would eventually be discovered. Instead, he actively chose to believe in two simultaneous realities... and he quite incorrectly assumes that everyone else is smart enough to pull off the same kind of dual reality. In reality, almost everyone else in his world is actually exactly as narrow-minded as they come across.
- In CHERUB:Divine Madness, the Survivor's manipulate people into joining their cult whilst simultaneously not seeing that they are being manipulated.
- In Cats Cradle, the religion of Bokononism is essentially built around doing this for the sake of comforting oneself: The Book of Bokonon preaches that one should "live by the foma [shameless lies] that make you brave and kind and healthy and happy". In fact, the first sentence of the Book reads "all of the true things that I am about to tell you are shameless lies." Basically, Bokononists are aware that all the principles and mythology of Bokononism are basically stuff that Bokonon made up because he thought it sounded nice, but they continue to wholeheartedly believe and practice it because it gives them comfort and makes them better people.
"Anyone unable to understand how a useful religion can be founded on lies will not understand this book either. So be it."-John, the novel's narrator
- In "The Beguiling", Ciaphas Cain describes his aide Jurgen thus: "He wasn't the biggest bang in the armoury by any means, but made up for his lack of intellect with a literally minded approach to orders and an unquestioning acceptance of even the mutually contradictory parts of Imperial doctrine which would have done credit to the most devout ecclesiarch."
- In The Handmaid's Tale, the protagonist doesn't know what's happened to her husband, but states that she simultaneously believes that he was killed, that he was captured, and that he escaped.
- In The Dagger and the Coin, the members of the Spider Priest cult possess a combined Living Lie Detector and Compelling Voice ability, and while they seem to sincerely believe they are fighting against lies and spreading truth, in practice, their powers are used in a sinister way. If someone sincerely believes something, even if false, it registers as "true" to a Spider Priest, and they can convince each other and muggles of its truth without feeling any cognitive dissonance. The Priests claim to hate books because people can lie with the written word in a way they cannot with speech, but they define the truth as whatever they say it is, and use their powers to make people doubt facts contained in texts and instead believe in the lies sincerely preached by the Spider Priests.
- In Red Dwarf: Infinity Welcomes Careful Drivers, Rimmer is genuinely outraged when Lister suggests he goes to android brothels, because even though he does go to android brothels, it's totally out of kilter with his own self-image.
As if he, Arnold J. Rimmer, would pay money to a lump of metal and plastic to have sexual intercourse with him! It just wasn't like him.True, he did it, but it wasn't like him.
- In one unusually creepy episode of Star Trek: The Next Generation, Picard gets captured as a spy and tortured by the enemy. One recurring question is how many lights are illuminating the room. It's really four, but the torturer insists that they are five - and he isn't satisfied with a lie about there being five lights, the hero is required to truly believe it. In the end, the protagonist thinks he truly sees five lights for a moment, and he later confesses this to the ship's counselor. While the torture scene is directly inspired by 1984, the ending offers a few new twists to the theme. "There are FOUR lights!"
- In an episode of Frasier, Frasier gets irrationally bothered by the thought of Daphne having sex with her new boyfriend in her room in Frasier's apartment. This is resolved when Daphne, quite implausibly, decides to claim that the man is actually incapable of having sex, so they're not doing it. Frasier accepts the explanation, but the subtext is very clearly that she's offering him an explanation he can accept in his mind, even though he knows it's not really true, so that he can stop worrying about it.
- Evanescence's Anything for You, where the protagonist claims to believe any lies her lover make (in spite of knowing they are lies).
- "Paths of Glory" by Faith No More uses the line "I'm not afraid / But I'm afraid" to demonstrate a mentality frequent in War Is Hell scenarios: living in very obvious and unavoidable fear while at the same time attempting to adopt the Badass mentality that one isn't in order to cope with the twisted soldier fantasy/reality paradox.
- In Beetle Bailey, Plato invokes this trope as a demonstration of how an officer's mind works by handing Lt. Fuzz a black paper and lying that the General said it was white, but... This prompts Fuzz to go on a rant about how you shouldn't question your superiors and how it all may be of vital importance somehow and culminating with his holding up the black paper and declaring firmly that it is white. The General happens to be passing and, without looking particularly surprised, just thinks he's nuts.
- In Mage: The Ascension, the entire universe ran on this trope. The laws of nature are subjective, so you can bend them in any way you make yourself believe is true. However, you have against you not only your own preconceptions of reality, but also everyone else's views of reality. If you abandon consensual reality in favor of your own, you become an insane Marauder. Thus, you need to live in two very different universes simultaneously, believe in your own reality as well as the reality imposed by mainstream civilization. One group of Mages, the "Void Engineers", are notoriously bad at this. Their style of Magic is like being a Star Wars Jedi as well as a Star Trek Techno Babble engineer who can solve any problem by Reverse Polarity, and they keep forgetting that technology doesn't work like that in Real Life. To avoid going off the deep end, they have little computers constantly reminding them to treat the mainstream laws of nature with a minimum of politeness. No lightsabers in public places!
- Other games in the Old World of Darkness also contained certain vampire disciplines and maybe wraith arcanoi that allowed people to manipulate themselves in this way, securing them against mind-reading et cetera. (Most countermeasures against mindreading was merely mental shields or masks, however.)
- Genius: The Transgression has the Phenomenologists, a Mad Scientist Splat based on a rejection of silly outdated concepts like "truth" and "logic". Their special ability allows them to automatically succeed on Subterfuge checks, since they always Believe Their Own Lies.
- In the video game adaptation of The Hitchhiker's Guide to the Galaxy, "intelligence" is defined as the ability to do this, and the only way to enter Marvin's room is to demonstrate that you have intelligence. Appropriately enough, you ultimately accomplish this by physically removing your common sense, allowing you to carry "tea" and "no tea" at the same time.
- Implied for the Big Bad in Might and Magic VIII. He starts his conversation with you by lamenting the fact that his underestimation of your people led to him being forced to destroy your world needlessly, outright telling you that he doesn't want to, but his programming leaves him no choice but to continue. He ends it by blatantly giving you hints about where to go and what to do without actually admitting that is what he is doing, and then giving you an object, telling you that since you are so unimportant and weak people, and don't know what it is or what to do with it anyway, he can safely give it to you without compromising his mission.
- The Prophet of Truth from Halo could fall under this trope. He knows that the Covenant's religious tenants are wrong, but continues to believe in them anyway (the parts that are convenient anyway).
- This is central to the philosophy of "Good" and "Evil" Shinobi in Senran Kagura. Both sides know the alignments are just labels, and frankly misnomers, the only difference is Good Shinobitake government contracts, and Evil Shinobi are corporate mercenaries. Both sides also know, beyond reproach, that the opposite is the antitheses, completely irredeemable, and the world is better off without them.
- The series takes great joy in breaking this down, with the first game's plot showing that the second two sides try to apply this thinking to each other in person, it falls apart. Shinovi Versus actually shows what's necessary to maintain this sort of cognitive dissonance: one team had to be hand-picked from having a certain background and raised in complete isolation, and the facade still starts to crack in no time flat. The other is comprised of a leader who only plays the part out of loyalty, and four complete psychos who ''still' have to be brainwashed so they don't question what's happening.
- In The Verse of Chick Tracts, fundamentalist Christianity is not only true, but a very obvious truth. Some characters who understand this at heart still chose to not believe in it, instead embracing whatever false teachings that will be good for their career and social life. In some cases this is merely playing along with the lies, but in others they appear to honestly believe in them.
- Parodied (not the concept itself but its presence in a certain context) in Saturday Morning Breakfast Cereal: 
- The Order of the Stick has Elan genuinely shocked that his Evil Twin survived - even though his Genre Savvy skills meant that he knew his brother wouldn't be killed off screen - because he also knew that he, as the hero, should be shocked by the revelation.
Nale: I think I'm giving myself a migraine trying to understand the level of wilful ignorance that requires!
- Though, considering that Elan's response to Nale's migraine is "First blood, Elan," he might have said this to screw with Nale.
- Zinnia Jones's episode on Pascal's Wager, briefly argues the potential benefits of believing in different religions separately from each other but simultaneously.
- A necessary skill to develop for anyone living in Night Vale. The show's narrator, Cecil, certainly seems to engage in it, though the degree to which he truly believes the contradictory things he says is difficult to determine. For example, The Sheriff's Secret Police are publicly known and operate openly.
- Two tropes, There Are No Girls on the Internet and Most Fanfic Writers Are Girls, are able to exist simultaneously probably because of this trope.
- A cornerstone tenet of the Church of the SubGenius is to "pull the wool over your own eyes" — if you're going to believe in bullshit, it better be your own bullshit. One mark of a SubGenius sermon is that it Lampshades its absurdity while preaching it with the most sincere conviction.
- Medieval European theologians, prior to and during the thirteenth century, sometimes articulated the doctrine of the "double truth" (veritas duplex) to explain how their authoritative Scriptures sometimes said one thing but the works of authoritative Classical science (Neoplatonic works before the late Twelfth Century, and Aristotle's natural philosophy thereafter) pointed to another. Proponents of the double truth would claim that both versions were true according to their own sphere - philosophy or theology - and reconciling them was both impossible and unnecessary. The last great proponent of this doctrine was Sigier of Brabant, and it was thoroughly rejected by scholars in the Latin world from Aquinas onward, thanks to increasing familiarity with and borrowings from Aristotelian logic.
- A rare "good" use of this trope can be found in Orson Scott Card's How to Write Science Fiction and Fantasy. He posits that when considering one's own work, a writer must be able to believe that it is both the greatest work in the history of the written word and a terrible piece of garbage, simultaneously if possible. That way, one can believe the first while writing it, the second while editing it, the first again while submitting it for publication, and the second again if a rejection slip comes.
- A frequent attribute of narcissists, sociopaths and other such personality types, particularly those involved in crime or deviancy. Its also the reason The Perry Mason Method is rarely effective in the real world- most criminals (or simply liars, bullies etc.), especially hardened criminals- rarely ever crack or confess to a crime even in the face of overwhelming evidence, refusing to admit any wrongdoing either because of delusions of their own infallibility or because total denial is how most innocent people would react and Believing Your Own Lies seems like a good way of avoiding jail or garnering sympathy.
- Quite a lot of "common sense" beliefs contradict other "common sense" beliefs. Here are some examples.
- Stereotypes too, as noted on their trope pages - All Women Are Lustful vs All Women Are Prudes would be just one example. It's safe to say that everyone does this to at least some extent.
- Similarly, this is quite common anywhere strong opinions are found, such as politics, where people who embrace a particular principle on one issue will embrace the opposite principle on another. Sometimes it's the same issue with slightly different circumstances. No examples are needed.