Leonard: Why not?
Teddy: Because your notes could be unreliable.
Alice has some agenda that leads her to tell a falsehood to Bob, such as introducing herself as a person named Claire. Alas, an unfortunate accident later, Alice gets Easy Amnesia! (Un)Fortunately Bob is present to tell her all she needs to know: as far as he knows she is really Claire, and having forgotten her real identity, she actually believes it. Depending on the tone of the work, hilarity and/or drama will ensue.
Compare Amnesiac Costume Identity, where Alice gets amnesia while wearing clothes that are not her own, with similar results, and Criminal Amnesiac, where Bob deliberately lies to Alice about who she is to get her on his side.
- One old Lois Lane comic had Lois get into a car accident while in disguise and become convinced that she was the person she was disguised as. In an ironic twist, she wound up hating Superman and Lois Lane, while also falling in love with Clark Kent.
- Inverted in The Addams Family, where the man impersonating uncle Fester turns out to be the real deal, amnesiac.
- In The Long Kiss Goodnight, Samantha is really a secret agent/spy. Because of her job, she had to lie about being together with a guy who was actually a mark; when she lost her memory, she apparently retained enough memory to believe that her last cover identity was her real name. She almost gets killed, instead being caught and tortured (and her old mentor gets killed because of this), but this torture allows her to regain her old memories and skills.
- Memento: As quoted above, Leonard, who has anterograde amnesia, relies on a system of notes and photos, which Teddy warns him could be unreliable. Turns out Teddy was right, and among other things, Leonard tricks himself into killing Teddy even though he's not the one Leonard is looking for.
- In Trap For Cinderella, Micky is told that her friend Domenica died in the same fire that disfigured Micky. Julia claims that she conspired with Domenica to kill Micky and have Domenica's face rebuilt to look like Micky's. Ultimately, it seems Micky was the one who survived the accident, then had her face reconstructed.
- In Unknown (2006), several of the amnesiacs remember being part of the kidnapping. Jean Jacket find that the kidnappers outside recognize his voice...
- The other film named Unknown (this one from 2011) combines this with Becoming the Mask. The film follows a character who's travelling with his wife, takes a cab and gets into a crash and wakes up in the hospital. When he makes his way back to the hotel, his wife is there, with a guy who claims to be him. Both his wife and the new husband swear they've never seen him before, and he has a full set of identification proving who he is. It turns out that he and his "wife" were assassins on a mission, and the crash apparently gave him amnesia, but he somehow remembered his cover identity and thought it was real. His employers sent in a replacement when his disappeared, using the same cover. When he learns all this, he decides he prefers the identity he woke up with, and helps to foil the assassination plot.
- Inverted in While You Were Sleeping: When Peter wakes up from his coma, the rest of his family tells him that he's engaged to Lucy, but Peter doesn't remember her at all. So the family concludes he must have Laser-Guided Amnesia. note Peter becomes skeptical of the amnesia explanation as he realizes that he still remembers everything else about his life—but he gives up and goes along with his family anyway.
- Sherlock Holmes manages to do it to himself in Michael Kurland's Professor Moriarty novel The Empress of India. He has a secret identity as a criminal, as a way of keeping an eye on the criminal underworld. When he suffers a Tap on the Head and wakes up in this lair, he deduces that this is his true identity, and proceeds to become a successful criminal.
- In Harry Potter and the Chamber of Secrets, Gilderoy Lockhart is a fraud who fabricated his entire career, but he successfully managed to keep the truth from getting out by generous use of memory charms on the people who actually did heroic things. When he unwisely attempts to cast another memory charm with Ron's broken wand, it malfunctions and backfires on him, giving him permanent amnesia and likely some brain damage. In the hospital he came to legitimately believe that the events in his career were true, since there was no one who knew the truth to explain to him otherwise.
- One episode of Insecurity had JoJo develop amnesia after getting hit by Alex's car while undercover as a drug dealer's girlfriend, and said dealer convinces her that she is said girlfriend.
- Happens in at least one Mission: Impossible episode. In the new series, Shannon almost ends up marrying the villain's son.
- A minor example in Smallville: during the period that Clark didn't know Chloe knew he had powers, he developed amnesia when a meteor freak accidentally erased Clark's entire memory rather than just the last few hours. Chloe talked him through his powers and told him he used them for good, but since she didn't know his origin, she assumed he was a meteor freak.
- Samantha Who? practically has this trope as part of its premise, as the protagonist has trouble finding out what was actually true about her pre-amnesia life.
- On Dark Matter, none of the main characters can remember their original lives beyond what their Galactic Authority 'most wanted' profiles in the ship's database tell them and go by numbers based on order of awakening from stasis. One is surprised to be captured by Jace Corso in "Episode 4" because that's who he thought he was; the encounter leaves him with no idea who he actually is or why he pretended to be a notorious criminal he's somehow identical to (other than Corso having an eviler aesthetic) or why he was on the crew of the Raza.
- "Episode 8" reveals the truth after the Expendable Clone made from One's genetic profile (Transfer Transit is a common way to travel via Brain Uploading to a temporary clone body in the setting) has a different face from his usual one. He was a wealthy industrialist named Derrick Moss whose wife Catherine was killed in a breaking & entering, and One's current shipmate Marcus Boone (Three) was the prime suspect. One concludes that he copied Corso's appearance through Surgical Impersonation to get close to and kill Three. Both One and Corso are played by Marc Bendavid, while Moss is played by Dan Jeannotte.
- Similarly, Six is unaware at first that he was an undercover cop named Kal Varrick infiltrating the Raza for the Galactic Authority, not actually a criminal like the rest of the (adult) crew sans Tagalog Kid Five, although in his case "Griffin Jones" was an alias fabricated for his cover and not a separate person running around..
- In Final Fantasy VII, the protagonist Cloud Strife narrates his past to the audience and the other characters at various points throughout the game. However, it turns out that he in fact lost his own identity and was simply narrating the past of his dead friend Zack, deluding himself into believing that was his own identity.
- The webcomic Picatrix has an example with a guy who believes himself on honeymoon with the heroine. Naturally, this doesn't end well for him when he makes advances on his "wife"...
- Then it's inverted, and more hilarity ensues.
- "The Forgotten", one of the early, unusual episodes of Batman: The Animated Series, had this happen to an undercover Bruce Wayne disguised as a homeless guy. He gets kidnapped by a greasy, overfed slavedriver who runs a mining operation, while Alfred is trying to find him. Very poignant episode, as Bruce gradually uncovers his memories and retakes his levels in badass.
- Another Batman example happens in the Batman: The Brave and the Bold episode "The Mask of Matches Malone": a hit on the head causes the hero to believe himself to be Malone, his undercover gangster identity.