Uh-oh. The Masquerade that you've worked so hard to build and maintain has suddenly been broken. Now a bunch of Muggles know that you and your entire family are vampires/werewolves/witches/what-have-you. But no problem. All you've got to do is whip up some mojo and give them a handy case of Laser-Guided Amnesia, right?
Well, no. See, turns out your spell/hypnosis/whatever, didn't work the way you'd intended. Sure, maybe it wiped the memory of a few, but there was this one guy whose memory remained intact. (Probably The Hero or someone close to him, but most certainly a character who has relevance to the plot. This trope is not wasted on minor characters.) For another a variation, the character in question may have their memory mostly wiped, but retain some crucial piece of information relating to The Masquerade. (Which they may not immediately recognize the significance of.)
Fake Memories usually have similar problems, someone always finds the holes.
The "partial erasure" version can result in a "I Know You're in There Somewhere" Fight attempt by a friend who tries to get the amnesiac to remember.
Compare Ripple Effect-Proof Memory (which may overlap) and Glamour Failure. Contrast Laser-Guided Amnesia, which is when the mojo works. Wistful Amnesia is a subtrope where a weaker version of this effect (that is, the victims don't remember more than that they've forgotten something) is directly caused by The Power of Love or The Power of Friendship. Amnesiac Lover can overlap with this trope if the "spot" was someone in a relationship with one of the victims. Amnesiac Dissonance (which is when skills that the amnesia allegedly should have erased come roaring back) also has overlap.
- In RahXephon, the Mulian mind control is shown to be imperfect when Hiroko realizes she has forgotten something really important when she meets Ayato again after his disappearance.
- Some of the girls from The World God Only Knows remember stuff after Elsie erases their memories. They usually come up with their own version of what happened to explain. This is explicitly because New Hell has power issues, and only erases the absolute minimum. This can bite Keima in the ass; for example, he took a girl to an amusement park for a date, which ended in a kiss. According to her memories, he ditched her halfway through for no reason whatsoever.
- When Albert Maverick Unpersons Kotetsu before framing him for murder in the 20th episode of Tiger & Bunny he slips up and misses mind-wiping two crucial individuals, Kotetsu's former boss Ben Jackson and judge Yuri Petrov/vigilante Lunatic. Both turn out to be vital in helping Kotetsu avoid capture by his former friends.
- In Code Geass, after having her memory wiped in the first season, Shirley finds a crumpled up letter that she had dropped beside her desk that tells her Lelouch is Zero. Then in the second season, she gets memory wiped again, but eventually regains her full memories after being accidentally hit by Jeremiah Gottwald's new Geass Canceler, which undoes the effects of both memory wipes.
- When Soul Society takes Rukia back, they mind wipe everyone and leave no traces of her existence behind. The only people unaffected are those who possess a significant amount of reiatsu: Ichigo, Chad, and Orihime.
- In Fade to Black, the antagonists possess a scythe that can erase the memories of anyone it cuts, as well as everyone's memory of that person. Ichigo is able to recover immediately due to his powers having been awakened by Rukia, and Kon is completely unaffected.
- The ending of Crisis on Infinite Earths shows that only the Psycho-Pirate remembers the multiverse or the details of the Crisis itself. Everyone else only has vague memories of a big battle and the skies turning red. He apparently attempted to inform people of what actually happened, only for people to assume he's insane, so they sent him to a mental institute.
- An Iron Man arc made it pretty literal: Tony Stark fired up a virus that erased all information of him from the Internet and memories from everybody around the world... and then it turned out that Doctor Doom still remembered. The amnesia virus was not able to make him forget that he had written a diary by hand (so it could not be hacked for deletion) that mentioned Stark.
- In the Empath: The Luckiest Smurf novel, the Psyche Master claims to have completely erased all of Empath's memories as an infant so that he would have no memory of ever being Papa Smurf's only biological son. However, the erasure procedure left only that memory of the infant Empath crying when he saw his father leave him in Psychelia just moments before the procedure started.
- In Path of the King when it becomes necessary to make Detective Dojima forget about the events related to Guilford's mansion, Tohsaka does an impressively good job of manipulating his memories via hypnosisnote (Her spot checks include using his trance to press him for info on possible conspirators or incriminating records that would jog his memory). However, he still notices that something is amiss because the reading of his car's odometer indicates about 50 kilometers more than the expected number.
- Fallout: Equestria - Project Horizons: Jetstream was so distraught by her lover Stonewing's death that she asked Vanity to remove the memories of him as she was going insane with grief. Vanity reluctantly agreed, but this only led to Jetstream's mental breakdown when their friend Big Macintosh dies. This triggers her to remember Stonewing and the realization of her lover and best friend's death drove her permanently insane.
- Finding Nemo: When Dory is swimming around the chain in the Sydney harbor, having lost grip on her memories again, she remembers almost nothing except that she "lost someone". She could either be referring to Nemo, who she has been watching Marlin frantically track down for the last few days, or Marlin himself, who has just left her behind - the reason she's now lost and confused in the first place. The memories return when she hears the name "Sydney", which she has been repeating to herself the whole movie. A bit of a different example, since Dory has a fairly accurate case of real-life anterograde amnesia; her memories simply fell apart because she lost the social connection she associates with them. The Sydney address, another connection she has to her friend, repairs them.
- Men in Black: When J meets Dr. Weaver in the Morgue, they vaguely notice that they may have met before, but dismiss it as Deja Vu. In the beginning of the movie, they had met, but K had wiped both of their memories.
- It's mentioned previously that a neuralizer leaves one feeling a vague sense of deja vu.
- X-Men: First Class: At the end, Xavier wipes MacTaggert's memory to keep the mutants safe from the CIA. All MacTaggert remembers is a few glimpses of leaves and Xavier kissing her.
- The protagonist of Paycheck has glimpses of what he was supposed to forget, along with the envelope full of notes, apparently because his last job used chemicals instead of the usual neuron-zapping, which is apparently complete.
- Jack in Oblivion (2013) has dreams of New York before the Scav invasion, despite his memory wipe to maintain secrecy. It's actually Genetic Memory, he's a clone.
- After his transformation to RoboCop, what remains of Officer Murphy's mind experiences flashbacks of his prior life despite his memory being wiped.
- The French sci-fi film Chrysalis features a memory-manipulating machine (capable of erasing and adding memories) which is used on the hero cop when he comes too close to a criminal conspiracy. He retains some flashes of information (and all of his fighting skills), which is enough to continue investigating. On the villain's side, the Big Bad implanted the memories of his raped and then torched daughter on a Replacement Goldfish young woman... and no matter how much he tried, he's unable to erase the memories of the rape (The Hero enters the memory manipulation room just as the doctor is in the middle of yet another try, and the man is having a Villainous Breakdown because the memories are doing a Rewind, Replay, Repeat of the rapist's face).
- Invoked in Eternal Sunshine of the Spotless Mind: the Laser-Guided Amnesia works by destroying the connections in the brain that are attached to the stored memories to be removed, causing the memories to fade away. When Joel changes his mind about having his memories of Clementine erased during the procedure, he tries to hide his memories of her within other memories where they don't logically belong. Unfortunately, the doctor performing the procedure is able to tell when he goes off the "map" and force him back onto it. However, in the end Joel remembers just enough of Clementine that he is able to find her again and they start their relationship anew.
- In Fantastic Beasts and Where to Find Them, Jacob Kowalski has to have his memory erased after the climax in accordance with magical law, but at the end he's shown to have made pastry replicas of various magical creatures, without knowing where he got the ideas from. He also seems to remember Queenie when she visits him.
- In Super Powereds, this is done deliberately to Nick, on the condition that he pass a Secret Test of Character
- In The Heroes of Olympus, Percy's memories of the events in the previous series are almost completely wiped at the beginning of Son of Neptune. The "almost" is his memory of his girlfriend, Annabeth, though it's dim. Just knowing her name motivates him to keep fighting and gradually regain his other memories.
- Mind-wiping in Artemis Fowl leaves "residual memories" which can be used to trigger total recall.
- In Matched by Ally Condie, witnesses to an event are ordered to take a mind-wiping pill, but the main character only pretends to and keeps her memory.
- In Spindles End by Robin McKinley, the two main adult characters try to hide attention from their young ward (the princess) by altering the memories of the entire village such that everybody "remembers" her coming to live with them a month earlier than she did. It's an almost perfect spell... and when the person it missed figures it out, all heck very nearly breaks loose.
- In Melissa Marr's Graveminder, Amity keeps a notebook to try to get around the town's magical amnesia. It is suggested, however, that she has trouble remembering to check the notebook.
- The Chronicles of Prydain novel The High King. Arawn Deathlord created the Cauldron-Born by putting dead bodies inside his Black Cauldron. They are mindless zombies completely under Arawn's control with no memories of their previous lives. When the defenses of Caer Dathyl were breached and the Cauldron-Born prepared to enter they saw King Math standing before them.
The deathless warriors of Annuvin halted as if at the faint stirring of some clouded memory. The moment passed and they strode on.
- Even while hypnotized by Achren, Eilonwy has vague memories of Taran and their time together at Caer Dallben.
- Fear and Loathing in Las Vegas gives us a non-magical instance; Duke mentions how some people who have a bad trip on LSD have trouble remembering anything save for a few scattered details. He mentions this in reference to the girl his attorney effectively drugged and kidnapped, Lucy, stating that even if they just set her loose and hoped her memory was fucked, she might "spend two more days in the grip of total amnesia, then snap out of it with no memory of anything but our room number at the Flamingo [Hotel]."
- In The Girl from the Miracles District, the Order had Robin's memories wiped out prior to the beginning of the story, but Robin retains a few scattered memories. Subverted as they're fake memories implanted specifically so that he wouldn't question his supposed backstory. There're also the Recurring Dreams which are the real missed spot in his memory wipe.
- In Diana Wynne Jones' Fire and Hemlock, the fairy queen wipes all traces of Thomas Lynn from Polly's life... except her friend Fiona's memory, which even Polly was unaware of.
- Coincides with Ripple Effect-Proof Memory in The 4400. The people who originally took the 4400 come back and capture a large number of 4400 children, stating that the future has not been changed as they had hoped and that they must place these children into new parts of history so that they can alter the future. One of them, Maya Skouris is wiped from all memory, with the exception of Agent Tom Baldwin, who continually sees her when his wife Alanna uses her powers on him. (She can psychically construct alternate realities for people.) He doesn't recognize Maya, but Alanna says that he must know who she is, since the alternate realities are created out of the subject's memories.
- This kicks off the main plot of the Star Trek: The Next Generation episode "Who Watches The Watchers"
- Twice on No Ordinary Family with the same characters.
- Daphne uses her newfound idea push powers to tell her inquisitive boyfriend not to ask about the family's special abilities. It works, but then a few hours later he broaches the topic again. So she pushes again, which works for a few hours again. Etc. She finally ends up telling him.
- Jim convinces Daphne to mind-wipe BF of his knowing about the family, so she gives him the instruction to "forget about when you learned I was special." This time it works too well, as he forgets their entire relationship.
- The memory drug in Torchwood, called 'Retcon', can sometimes leave nagging little details in the victim's mind. If they're distanced from all the weird things they've seen, it won't be a problem, but if something triggers it the memories come back. This is how Gwen re-learns of Torchwood in the pilot after Jack wipes her mind.
- Played with on House of Anubis, When Fabian gets his amnesia curse. At first, he is still able to remember enough, like who Nina is, even though it does take a little work to trigger these memories. Though, eventually he does lose his entire memory, including his name.
- A character in an optional side quest in Deus Ex: Human Revolution had augmentations installed to keep him from remembering certain missions. However, fragments remained, which let him to knowing that his mind was being tampered without his consent or knowledge.
- In Persona 3, ordinary people who don't experience the Dark Hour have their memories revised afterwards to explain anything strange that occurs during the Dark Hour. (Which they might notice after it passes). In one scene, Mitsuru mentions that so many people are coming down with Apathy Syndrome that the memory revision can't keep up.
- At the end of the game, either the protagonists (in the bad ending) or the entire world and the protagonists (in the good ending) have their experiences of the Dark Hour, as well as all the bonds of friendship and Character Development that occurred because of it, erased from their memories. Everyone, that is, except for Aigis, who explicitly remembers everything. Depending on which ending it is, the character's situation is either wistful or downright Fridge Horror, because in the bad ending she knows that The End of the World as We Know It is hours away from happening but there's absolutely nothing she can do to stop it, and she can't even tell her former friends about it because they don't even remember who she is.
- It's also implied to have missed to the Main Character in the good ending, since he/she can speak to Aigis about it in the last two days before graduation. However, since the narrative skips from the aftermath of the Final Battle to the day before graduation, it's ambiguous whether he/she retained all memories along with Aigis and simply kept quiet about it for three months, or whether the memories came back on that specific day.
- Also in Persona 2. At the end of Innocent Sin, Philemon recreates the world at the catch that everyone will forget everything. Tatsuya Suou, The Hero of Innocent Sin, keeps his memories out of sheer willpower, but is forced to give them up at the end of Eternal Punishment. Big Bad Nyarlathotep, of course, remembers everything due to his supernatural status and restored the memories of the Ax Crazy Pyromaniac Tatsuya Sudou.
- The first Knights of the Old Republic had this as the backbone of the plot. Revan's fragmented memories, as spied on through Bastila via the Force Bond were supposed to lead the Jedi to the Star Forge with your Player Character being none the wiser.
- Of course, in this case the amnesia might or might not have been accidental. Depending on which it was, the trope is either invoked ( if the Jedi deliberately wiped your memories, the intention must have been for it to miss spots so that they could be used to find the Star Forge) or exploited ( if the amnesia was an accidental result of the circumstances of your capture, the Jedi took advantage of this at least as soon as they realized what was going on, and potentially as soon as they realized the possibility of this trope).
- While closer to recreating the world entirely, the end result is that everyone in One Shot loses their memory of previous sessions when a new game is created. Everyone except Niko, who is instead from another universe, and still remembers the player's name, if not who the player is or that they even exist. A solstice run further reveals that Niko can recover further memories with some effort, and that they find knowing of the player without understanding why or anything else about them is extremely disconcerting.
- Dangan Ronpa:
- When he gets sick with a high fever in Chapter 5, Makoto remembers that he should want to stay in the school, rather than escape it. He doesn't quite understand the context or the ramifications of this until the final Class Trial.
- Kyoko reveals that she can't actually remember what her Ultimate talent is, but she remembers enough that she knows the Mastermind has tampered with her memories.
- In Genocide Man Joey reveals that his tweaked augments make him immune to the Lethe Protocol they use for discussions of things so terrible that plausible deniability isn't enough. He takes advantage of that immunity to jog Jacob's memory of voting to use the Guyaquil Complex that killed a billion people.
- In X-Men: Evolution, an entire sports stadium of people learn about the different mutants among them and their powers. To maintain their secret identities, Professor X tries to erase everyone's memory of the night, but blacks out before he can finish erasing Principal Kelly's mind. Principal Kelly later goes on to be very anti-mutant.
- In one episode of Futurama it looks like Fry was ground up into sausages and Leela goes to a memory erasure clinic to relieve the pain of his death. She is told before the procedure starts that it only hides memories, it doesn't remove them entirely and she might accidentally remember again. Meanwhile Fry is actually living among a Neanderthal tribe with blunt trauma-induced amnesia. Naturally, they both regain their memories upon meeting one another again.