Ripple-Effect-Proof Memory

"Guildenstern: You know your way around? The Player: I've been here before. Guildenstern We're still finding our feet. The Player: I should concentrate on not losing your heads. Guildenstern: Do you speak from knowledge? The Player: Precedent. Guildenstern: You've been here before. The Player: And I know which way the wind is blowing."

- Rosencrantz and Guildenstern Are Dead

When Time Travel is used to "rewrite" past events, the main characters will typically retain their memory of the original timeline, i.e. how everything went the "first time around", even though that version of events no longer happened. Everyone else will only remember the new reality, but not the main characters. They're special. After all, how can they Set Right What Once Went Wrong if they don't know something went wrong?

Often justified by saying that it doesn't affect time-travelers -- memory has Ontological Inertia. Following this logic, there should be alternative versions of the time-travelers who do remember the new timeline (that is, unless they prevented their own births). This is almost never addressed, but leads to the common Timey-Wimey Ball theory that says that the new versions are replaced by the time travelers when they get to the age where they started time-traveling. This holds even when there's actual evidence that there was a "new" version of the character in the new timeline -- even if all of the time-traveler's family and friends now know him or her as a zeppelin racer extraordinaire, he/she doesn't remember any of it, despite the fact that someone had to win those trophies. This makes it less like the past was literally changed and more like the molecules of everything in the universe except the main character were re-arranged into a configuration consistent with a different past.

Moreover, there are instances where characters who didn't time travel get Ripple Effect Proof Memory anyway, which may or may not be justified with some Applied Phlebotinum. However, the only way to really avoid these problems is to set the story in a universe where You Already Changed the Past and that can be pretty hard to pull off, especially on a regular basis.

Ripple Effect Proof Memory may cause a Psychic Nosebleed, when someone whose memory isn't completely 'proof' gets an 'update' on a new lifetime and the mental stress from trying to contain memories from a large number of timelines actually harms the physical body. This might happen even if memories are the only thing that carry over from shift to shift and the time traveler is no longer in his or her original body. The technical term for this is "the time travel clone memory feedback problem". We're working hard to find a cure.

Ripple Effect Proof Memory is inherent in any and all Groundhog Day Loop, Mental Time Travel, and It's A Wonderful Plots. As we already have pages on them, instances of them shouldn't be included here. Individuals with a Ripple-Effect-Proof Memory may be the only ones who recognize a Ripple Effect Indicator for what it is.

The name refers to the "ripple effect" from the Back to The Future films.

Anime & Manga

 * In Haruhi Suzumiya, Haruhi . Nobody has ripple proof memory and Haruhi has the least ripple proof memory of all. The rest of the Brigade do however, at an increasing rate. They've gone through . Yuki, though, apparently.
 * And in Disappearance, when . Everyone else does not, however.
 * Deconstructed in Higurashi no Naku Koro ni. It's in fact the main source of conflict during the second season.
 * Occurs in XxxHolic and its sister series Tsubasa Reservoir Chronicle several times due to some major futzing with the time-space continuum, but the most obvious example is who is Ret Goned from the memories of all but a few people once.
 * Pretty much all instances of Time Travel in Pokémon. In Arceus and the Jewel of Life, Ash & co. remember events as they happen after Dialga sends them back through time, but they also remember the original history that necessitated the trip to start with. Arceus itself is subject to Delayed Ripple Effect, and nearly blasts them before its memories catch up.
 * In the Japanese version of the Celebi movie no one remembered as well. The dubbers felt that it too closely mirrored the first movie, and elected to change it. They discuss the matter, and an additional scene with   reflecting, in the commentary.
 * In the season 9 (Battle Frontier) episode "Time Warp Heals All Wounds" May, her Squirtle, and Meowth travel back in time to save a man's life
 * In Serial Experiments Lain episode 11,  alters history to remove some rumors around school about Arisu but leaves Arisu's memory intact. After all, memory is just data. Arisu finds the whole experience a bit unnerving.
 * In Episode 117 of Yu-Gi-Oh! 5D's, it is revealed that Yliaster were able to alter history. When they did so, only the Three Emperors, the Signers and those within their protective fields, and Team Ragnarok (who held the Polar God Cards), were seen to be aware of the changes.
 * In the Clannad anime adaption,.
 * By the end of Puella Magi Madoka Magica, no one remembers and her very best friend. On the other hand, since she's now a transcendent law of the universe, she remembers everything that was, that will be, and even that which can't possibly exist.
 * Before that, though,.
 * Okarin from Steins;Gate has one of these.
 * Played more plausible than most examples since he usually gains no more than a weeks worth of memory at a time and it still disorients him immensely to the point of Idiot Ball.

Card Games

 * In Chrononauts, certain Identities have Ripple Effect Proof Memory, but they come from different timelines. These players win by restoring history to however they remember it. Others try to change history from our (and their) history to one which they prefer -- such as Betty, who wins by saving JFK in 1963, and Yuri, who tries to make the USSR win the Cold War.

Comics

 * This was in The Authority, when The Doctor has to relinquish his powers to one of his predecessors (one who was stripped of them for being a depraved omnicidal maniac). The old Doctor stops in the middle of the fight to point out that he can freely travel through time, threatening them with "imagine fighting someone who could shoot you as you emerged from your mother's womb or hold a pillow over your face in a retirement home." He then adds "worse still, imagine the local doctor, back when you were in high school, giving you a funny feeling you'd carry around for the rest of your natural life". He doesn't go as far as raping The Engineer (or if he does it's off-page, or has been changed in the reprinting) but the comic does take a panel to show him kissing her on the back of the neck. He asks her "Hello again, Miss Angela Spica of class 4B. Remember me?" which starts her crying and whispering "oh my god..."
 * In the Marvel Universe, Bishop has occasionally ended up like this, due to doing a bit more time-travel than is really healthy... After the 'Age of Apocalypse' timeline was destroyed, and everything went back to normal, he experienced some occasional 'regression' into memories of the now-defunct timeline -- up to and including attacking Beast and Cyclops, who were evil in the other universe.
 * Likewise, explained within the Astro City series, as anyone jumping into the 'empyrean fire' of the time stream seems to be immune to the effects of any temporal changes. That such a thing also happens to impart the user with superpowers and would be the only way to make the local pastiche of Superman/Captain Marvel/generic hero work without a paradox is just an extra bonus.
 * Oddly, some people in the Astro City series have at least some resistance to the Ripple Effect. A viewpoint character He remembers the old timeline only when he dreams.
 * In the Marvel mega-crossover event House of M, Wolverine and a new character called Layla are able to remember the original timeline, how things were before the Scarlet Witch rewrote history. Layla is a mutant with Ripple-Effect-Proof Memory (and the ability to undo time travel's effects on the memories of others) as her stated superpower. Strangely enough, Spider-Man gets the feeling that things aren't quite right with the world and writes a journal detailing the events of the original timeline, but no reason is given for that.
 * Bart Allen, the hero known as Impulse, Kid Flash II and (briefly) Flash IV, has a permanently Ripple-Effect-Proof Memory as a result of being sent from the future. On the more notable occasions Wally West's wife was removed from time, the entire Flash lineage was erased and scary future versions of the Titans went back and changed the future they came from, and he was entirely unaffected.
 * Tom Strong featured an aversion of this trope. His greatest adversary managed, at one point, to take over the time stream, and used some new technology to open a time gate, pulling versions of himself from all points in his life through the gate and into the timeline. He ended up with the backflow of over three hundred separate memory streams converging on his head all at once- luckily, the Clock Roach guardian he defeated to take over the time stream felt generous enough to send them all back, with the note that the youngest of them will have to go through every single one of the summonings and unsummonings. The mental chaos this event produces drives the villain to madness and probably leads to his downfall.
 * In the infamous One More Day, Spider-Man makes a deal with Mephisto in order to save Aunt May's life, which rewrites decades of Marvel continuity to create an alternate timeline where he was never married to Mary Jane and he never revealed his secret identity. However, despite this, Spidey is still shown to remember the events of the original timeline. It's even a plot point in certain issues, where characters that knew Spidey's identity beforehand (such as the Fantastic Four) have forgotten, and only by showing his face will their memories be restored. The only people who remember Spidey's identity from the beginning are Mary Jane and his clone Kaine, and the recent One Moment In Time reveals that Mary Jane also remembers the original marriage. Deadpool is also hinted to remember due to the fact that he demolished the fourth wall long ago, but he's never yet used it beyond a Take That.
 * In the Sonic The Hedgehog comics, this comes up during the Mobius: X Years Later stories. After the timeline gets altered, some handy Applied Phlebotinum allows Sonic and several of the other heroes to remember the unaltered reality. The same Applied Phlebotinum also allows Lien-Da to remember as well, while King Shadow is able to remember simply because of his Chaos powers, which are themselves a loose form of Reality Warping.
 * Done in Paperinik New Adventures where, after a time rewrite, a select few get occasional flash-backs to how reality was supposed to be. Odin Eidilon then checks his own memory against a backup memory he had kept in a time-proof safe to confirm his suspicions.
 * Humorously Averted in Alan Moore's one-off "Doctor Dibworth's Disasppointing Day". The titular scientist invents a Time Machine and tries to test it by making at first minor, and progressively more drastic, changes to the past. Each time he does, the narrative helpfully informs us that nothing changes, while the artwork shows the results of massive changes to history. Doctor Dibworth does briefly consider that his own memories are altered as a result of changes to the past, but dismisses that idea as unlikely.
 * Played with in Flashpoint where Barry Allen (The Flash) wakes up one day to find the world is completely different, and the least of the changes is that he never gained superpowers. He's the only one who remembers the previous timeline, but this memory is slowly being erased and replaced with memories of the new one. Thus it takes Barry almost the entire series to realize that
 * Also completely averted with the ending, in which the timeline is changed again (to one very similar to the "correct" timeline, but with some differences.) This time, no one remembers the old timeline, including Barry

Fan Works

 * Time Travel stories are rife in the world of Harry Potter fanfiction. One almost univeral common factor is that no matter how much the timeline changes, Luna Lovegood remembers the old one and has no problem with the idea of multiple timelines existing.
 * Ichigo has this  in Hogyoku Ex Machina after time traveling..

Films -- Animation

 * In the animated film Meet the Robinsons, Lewis retains his memory of his entire adventure, even though through the course of the adventure, he takes several steps to prevent the film's villains from existing. Logically, this would mean the entire plot of the film never happened, though not addressed in the film itself. He's a really good inventor.

Films -- Live-Action

 * Naturally, the Back to The Future trilogy. It is a bit strange to note, though, that while memory is proof against the ripple effect, ontology is not: Marty remembers his own timeline in the first movie, and yet he comes close to literally fading out of existence as history is pushed off-track. It may be that in BTTF, memory is not proof against the ripple effect per se, just a bit insulated from it, and like Marty's photograph, will fade slowly as the timeline diverges. Or it's just a big Timey-Wimey Ball.
 * Marty almost fades away in the first film because he almost changes the timeline to one where his parents never got together and thus he was never born. The timeline he ends up creating by the end of the movie is one where his parents DID meet but under different circumstances and thus he WAS born, but his parents are happier. If memory and ontology were both immune to the ripple effect, then what would be left to change as a result of time travel?
 * The lack of an alternate version of Marty is averted, however. It is implied that there is an alternate version of Marty in the new timeline, but Marty never meets him because Biff sent him Off to Boarding School.
 * If that Marty really existed, it'd mean Marty would meet an alternate self in every reality he created.
 * In the novelization of Part III, it's also implied to work in the other way. Marty gets help from 1955 Doc to go back to 1885 and save the 1985 Doc. When he gets there, 1985 Doc asks him not only how he got there, but also who dressed him in such ridiculous clothes. Marty says that 1955 Doc did. At which point Doc remembers.
 * Of course that could just as easily be explained as Doc not really remembering (to him) a thirty-year-old minor event until Marty reminded him.
 * Happened in Source Code. The protagonist is on a mission to stop a bomb from blowing up a train. He has 8 minutes. Every time he fails (and hence dies), when he is reset, he remembers what happened in the previous run. This is Justified by the nature of the Source Code. However, there is an interesting twist at the end.
 * The Butterfly Effect However, it should be mentioned that each time the protagonist changed the past, he received the memories of his own life (in the new timeline) up to the present. However, the memories weren't just there -- they arrived as a searing burst of information (being physical written into his brain), and co-existed with his old memories, giving him a Psychic Nosebleed.

There is one scene where another character has ripple-proofing, despite the fact that they shouldn't; the protagonists goes into the past and impales his hands on some spikes, to give himself Jesus-like markings in the future, so he can prove to his friend he's not lying. To his friend, they seem to have just appeared, which didn't happen to any other character in the film.
 * The movie Frequency gives this a Hand Wave; after the main character inadvertently changes the past, he talks about how he sort of remembers it both ways. Though this is then dropped for the rest of the film, where he only remembers the original timeline after
 * The disadvantages of this are touched on at the end of Time Cop, where the hero is surprised to learn he now has a wife and son....
 * Sandra Bullock's character in The Lake House seems to have this. Of course, the film is one big Timey-Wimey Ball. The film could have been a knotted Stable Time Loop if there wasn't that one tree and if
 * In the Disney film Minutemen, the time travelers have this, but the people who asked them to change the past don't. Fortunately, they thought of this, and took a video of something that was never going to happen with them to the past. Apparently, even inanimate objects have Ripple-Effect-Proof Memory!
 * Godzilla vs. King Ghidorah, the only Godzilla movie so far to feature time travel, uses this trope. After the timeline has been altered in WWII so that King Ghidorah attacks Japan for decades instead of Godzilla, the main characters note the difference. Later when it turns out that Godzilla does still exist in this universe except bigger, they note they are the only ones who can identify him and even realize the change in size. The filmmakers seem to have forgotten this when they made Godzilla vs. Space Godzilla and everyone acts as if the timeline never changed and Godzilla hasn't been replaced with Ghidorah...yet references to Ghidorah are made and Godzilla is still at the larger scale.
 * Star Trek: First Contact. The Enterprise can see the Borg!Earth timeline, but since they're in the wake of the time disturbance caused by the Borg Sphere, they're unaffected. It's strongly implied that they'd vanish from existance had they not went through the time aperture themselves.
 * Agent J has a ripple effect-proof memory in Men in Black 3.
 * Brazilian film O Homem do Futuro (The Man from the Future) has protagonist Zero accidentally going back 20 years to the prom that ruined his life. So he tries to Set Right What Once Went Wrong, and vanishes as history is changed, waking up back to the present day... where he became rich, but is a Jerkass and the love of his life hates him. So he goes back again, and after leading things to go back the original way he vanishes again... returning to 2011 with memories of the entire time travel ordeal.

Literature

 * The third book in The Dark Tower series subverted this. Roland was going insane because he was remembering two timelines, one where, and one where he didn't. Of course,
 * In Ray Bradbury's A Sound of Thunder, several time travelers to the past realize that they have changed history when they return to the future and notice changes that no one else recognizes.
 * In The Lathe of Heaven, George Orr is the only one who knows reality has changed. Of course, that makes sense, as his dream causes it. It is also discovered that anyone in the room with him when he is hypnotized into dreaming a change also knows it. That makes slightly less sense, although since his subconscious is involved and the method used is not machine based, it certainly is possible. Even though other people with him can know, they are still not sure it happens unless he reminds them or it is a major change.
 * Robert Silverberg's Up the Line discussed this and other temporal oddities fairly well.
 * Robert A. Heinlein's The Cat Who Walks Through Walls has an incident where the protagonist is told a nasty event from his past has been removed, thanks to time travel. He protests that he still remembers it, but this is explained as "a memory of a memory", which will fade.
 * Used to blackmail the title character in the Thursday Next series when her husband is "eradicated" by the villains, and she is the only person who remembers him. Played with a lot along the way. There's even a therapy group for other people in this situation. (Everyone else just thinks they're insane.)
 * One recent short story featured a American sniper who is equipped with an experimental time machine sent on a mission to kill Osama bin Laden before 2001, comes back and finds the situation worse (without bin Laden inspiring a spectacular, but limited, attack, the terrorists who did launch an attack were more careful and the result far greater). So he tries again, going a little further back in time, and the situation is even worse. So he tries again. And again, and again. After offing Mohammed didn't work, he's finally trapped in 1st Century Palestine when his time machine breaks after trying to kill Pontius Pilate.
 * While it covers dimensions more than time, all Travelers in The Pendragon Adventure retain their memories of how their worlds used to be. Their acolytes are the same. This is a good thing, because starting from around the seventh book of the series, the world begins to change severely.
 * In The Stainless Steel Rat Saves the World, Ripple Effect causes your memories of the other timeline to change rapidly. If you don't exist in the present timeline and you forget who you are, you literally fade away! The Special Corps created a countermeasure in the form of a device you stick on your head that reminds you of who you are every few seconds to keep you from vanishing outside your own timeline. Since the time machine he was using to Set Right What Once Went Wrong could only carry one person (him,) Jim took several other scientists' devices to temporarily overwrite himself!
 * This plays a big part of the plot of A Game of Universe, as the protagonist has no Ripple-Effect-Proof Memory, only occasional "afterimages" he can see with magical vision. He doesn't realize any time travel is happening until the person responsible shows up and explains that the only reason the protagonist is alive is because he's been hitting the Reset Button every time something goes wrong.
 * Time travel is used several times in Animorphs:
 * Book 11 has Jake, the narrator, being the only one who remembers the alternate timeline. This is explained as
 * Explicitly referenced in another book in the series, when the Drode first "restores" the Animorphs' memories in a way that lets them still remember the last five or so minutes of conversation but not any other details about the world in which they now live, then mentions that their memories will be "buffered" as they follow Visser Four through history. The Time Matrix also seems to confer this ability on to everyone who uses it (at least for changes they make using the Time Matrix), including Visser Four himself.
 * Cassie is shown in Megamorphs #4 to be a temporal anomaly who has this ability by default--if her timeline is altered, she gradually becomes aware of the discrepancy and subconsciously causes the alternate timeline to fall apart.
 * Justified by Chronos in the Incarnations of Immortality series. As the Incarnation of Time, him and his memory would be impervious to any ripple effects. (Within reason: He isn't allowed to affect the past in a way that would prevent him from becoming Chronos.)
 * In John Dies at the End, the Living Shadow monsters regularly jump around through time and change things for sinister, unknowable reasons. However, random people end up with memories from before the timeline was changed.
 * In Xanth, Lacuna wishes for a more interesting life, changing a big chunk of history in the process, but only she and a handful of others remember this.
 * In the concluding trilogy of the Sword of Truth saga, a spell called Chainfire erases almost everyone's memory of Kahlan, but Richard is protected because he was holding the Sword of Truth when the spell was cast. This is implied to be one of its original purposes, besides just being preternaturally sharp and conferring the skills of past wielders on the current wielder. Ultimately, the Boxes of Orden are the only way to repair the damage, and that was their original purpose.
 * In ((The Golden Spiral'', only Abby remembers how things were "supposed" to be after explained because she's been "outside" of time. she can also sense when he changes something. later she learns that she can "fix" someone in reality( the can't be altered) and restore their ' true' memories by
 * The eponymous Nobody in Nobody Gets the Girl is a product of this for most people when they experience this fade away. But the limitations are he can't be seen by anybody who doesn't believe he is there, and he can't move objects when he is being observed by someone who can't see him. But he can be observed by video cameras.
 * John Barnes's short story Things Undone varies this depending on the size of the changes made. If something small changes, certain antisocial people will only remember the way the world used to be, and everyone else will only remember what it becomes. It turns out a big change
 * In Dirk Gently's Holistic Detective Agency, time is altered to destroy most of Coleridge's poem "Kublah Khan" (which now ends at the line "And drunk the milk of paradise"), in consequence preventing a murder and the retroactive destruction of humanity, as well as introducing a composer named Johann Sebastian Bach. Only the time-traveling main characters remember the original reality.
 * In Star Trek Department of Temporal Investigations, the titular department keeps records protected by phase discriminators, shielding the data from alterations in the timeline. Although the agents themselves will have no knowledge of the previous history, they can research their own files to determine if changes have been made. In the novel Watching the Clock, there's also a subplot that takes two of the protagonists to a Place Beyond Time, leaving their memories of another character intact when she suffers a Ret-Gone.
 * In Johnny and The Bomb everybody but Johnny forgets their time travel experiences, although Kirsty remembers them again after finding a piece of physical evidence.
 * Intentionally invoked in Night Watch. Thanks to narrativium, history is mutable and subject to popular perception, so it doesn't matter if Vimes' memories of the "original" version are different as long as events play out roughly the same.

Live-Action TV
"Riker: You mean we could've come into this room, sat at this table and had this conversation a hundred times already?"
 * Doctor Who
 * In "The Time Meddler", the Doctor's companions suppose that, should the Monk succeed in changing history, their own memories would instantly change. While this might seem to exclude the Doctor from this trope, the balance of evidence points the other way, and there's no way for the companions to be doing anything more than guessing. Of course, many fans will angrily tell you that "The Aztecs" conclusively proves that you can't change history at all in the Whoniverse, so the question is moot. Both examples require that you discard the overwhelming evidence in the other direction, of course.
 * The closest the new series has gotten to a definitive stand on the issue is to say that the Time War was "invisible to lesser beings, but devastating to higher forms." The Word of God, so far as anyone can piece together from various comments, is that more highly evolved species, particularly the temporally active ones, have ripple-proof memory. Whether similar status is conferred upon humans who have time traveled is likely but uncertain. Comments by Russell T. Davies explicitly name the Time Lords, Daleks, Gelth, Nestene Consciousness, and the Forests of Cheem as "higher beings".
 * In Flesh and Stone, it is explicitly stated, first through events, and later through dialogue, that a time traveling human gets ripple-proof memory too. "You're a time traveler now, Amy. Changes the way you see the universe. Forever. Good! Isn't it?"
 * They also establish, though, that this mostly applies to timeline changes from outside your own era, which is how
 * Last of the Time Lords: In what is known to Whovians as, characters aboard the experience this; it is explained that their proximity to the  allows for this.
 * The Stolen Earth: A representative of the Shadow Proclamation explains that, in the wake of the Time War, the lesser races only know of the Time Lords at all from "legends passed down from the higher beings".
 * Cold Blood adds a further complication: if a change to history undermines a time traveler's own personal history, they are only partially protected: the relevant memories will change, but the traveler can resist this through concentration. Or so we're told: the traveler in question fails to resist the change, so it is not clear that this ability is anything more than theoretical.
 * The Big Bang adds yet another wrinkle: growing up near a crack in time can do unusual things to someone's memory. If they end up having their personal history changed, the original memories will still be present, buried in their subconscious. This effect remains even if they become a time traveler.
 * The effects of proximity to a time crack are all-but-confirmed in "The Wedding of River Song", where Amy is again able to retain memories of timelines that never were.
 * Journeyman
 * Stargate SG-1 ("2010", "Moebius") and Stargate Atlantis ("Before I Sleep", "The Last Man"). Both follow the logic which states that the time-travelers should have alternative counterparts in the new timeline. Their earlier counterparts always seem to conveniently end up dying.
 * In Stargate: Continuum, a Delayed Ripple Effect almost gets the team (minus the already-erased Teal'c and Vala) before they enter the Stargate. It turns out being in a wormhole at the time of the ripple effect makes you Ripple-Effect Proof. Who knew? Unusually, this example shows alternate versions of the man characters, except two -- one was never born, and another died a hero some time ago. A third is only ever "seen" from the wrong side of a phone line.
 * In "Window of Opportunity", O'Neill and Teal'c have Ripple-Effect-Proof Memory. Might be partly due to the fact that time technically kept going, and the looping turned out to be somewhat selective.
 * In "Moebius", actually, the team didn't remember the time that they had erased once they set wrong what once went right. But their past selves had made a video tape to deal with this very problem, which convinced each of them that time travel had occurred and they needed to change it.
 * Star Trek, being deeply in love with time travel, has had many examples of this:
 * An example where this occurs to characters who didn't time travel: "The City on the Edge of Forever" from Star Trek: The Original Series. Hand Waved later on as being due to their proximity to the Guardian of Forever.
 * Star Trek: The Animated Series with "Yesteryear", which also featured a trip back through the Guardian of Forever that changed history. Only the time travelers remembered the original timeline in which Spock existed.
 * The New Voyages fan episode In Harm's Way treads similar ground; history is altered such that the Federation is fighting a losing war against a fleet of Doomsday Machines, and Kirk and his crew are stationed aboard the USS Farragut, with a Klingon first officer. Only Spock, who was engaged in studying the Guardian of Forever when the change took place, remembers the way things are "supposed" to be.
 * Lampshaded in the Star Trek: Deep Space Nine episode "Accession": Kira mentions an unfinished work of a poet who disappeared long ago. Sure enough, he shows up five minutes later. By the end of the episode, he's been sent back in time, and she's shocked to discover that the poem is now finished and again shocked that she remembers it ever being unfinished. "The Prophets work in mysterious ways."
 * Lampshaded again when the Deep Space Nine cast visits "The Trouble with Tribbles". Sisko complains that if he changed time, he would have been the first to notice. The Time Agents complain that people always say that. (Thankfully, he didn't change time in any significant fashion. Probably.)
 * Odo did bring a tribble back with him -- when they had already been driven extinct, which is not a temporal paradox of any sort (and harkens back to Kirk's saving of Humpback whales in Star Trek IV), but would almost certainly constitute a violation of whatever laws the Federation has regarding the transport and breeding of endangered and/or environmentally dangerous species. Given the history of Klingon interaction with tribbles, it might even have led to a major diplomatic incident..
 * In Star Trek Online, there are "Tribble Extermination Squads", which is considered one of the lowest positions a Klingon can hold, short of being kicked out of the military altogether.
 * In another episode of Deep Space Nine, Sisko, Dax, and Bashir are sent back to a tumultuous period in Earth's history and inadvertently change things such that civilization collapses. The ship in the present from which they'd departed was shielded from the timeline alterations by the same effect that sent them back in time. As before, they return to find history only mildly altered (in this case, a historical figure now bears an uncanny resemblance to Ben Sisko).
 * Two similar episodes from Star Trek: The Next Generation ("Yesterday's Enterprise") and Star Trek: Voyager ("Time and Again") feature history changing without anyone remembering it, but with the local telepaths/mysterious wanderers having odd feelings about something being out of place.
 * There's also the TNG episode Cause and Effect, in which the Enterprise gets itself trapped in a time loop and end up repeating the same day over and over. They DON'T know they're repeating it however, until various hints and a creepy sense of dÃ©jÃ vu start becoming apparent, and they catch on:


 * The crew are then (somehow) able to send a single one word message into the next timeline via implanting a message into Data's positronic net, thus giving them a one-shot chance at changing the future and avoiding the loop - all they could send was one single word, and hope that would be enough for Data to get the hint and change future events.

"Crusher: Computer, read the entire crew roster for the Enterprise. Computer: Dr. Beverly Crusher. Crusher: Have I always been the only member of the crew on the Starship Enterprise? Computer: Affirmative."
 * In Star Trek: First Contact, the Enterprise becomes Ripple Effect Proof due to getting caught in the Borg ship's "temporal wake" before they followed it back through time.
 * No one remembered history changing back from "Yesterday's Enterprise", either -- it seemed to those aboard the Enterprise-D that nothing had happened. But the round trip of the Enterprise-C had an unintended consequence which would surface for a later season.
 * It's not clear just how much Guinan remembered of the timeline change: she calls the bridge to make sure everything is OK and then asks Geordi to tell her about Tasha Yar. In the original script of "Redemption, Part II" she says she has a vague memory of Tasha asking her something.
 * Guinan likewise had flashes of the "proper" timeline in the alternate one of that episode. Guinan's time-sensitivity is eventually explained in Generations as a side-effect of the "time" she spent in the non-temporal world of the Nexus.
 * A particularly convoluted example from a recent novel involved Scotty going back in time to save Kirk from "death" on the Enterprise-B. Since Kirk wasn't in the Nexus to be pulled out by Picard, the Enterprise-D was destroyed, and the Borg succeeded in changing history in First Contact. In the new timeline, only Scotty (and an accomplice?) recall the original timeline -- and they're the only non-assimilated humans. Presumably the Borg know, but they aren't talking.
 * During the "Temporal Cold War" arc on Star Trek: Enterprise, Crewman Daniels, a time traveler from the far future, zaps Captain Archer to his own time to save him from capture by the Suliban. They both arrive on a devastated future Earth whose technology hadn't progressed even to TOS levels, where the Federation had never been founded (and, it's implied, the Romulan Empire became the dominant force in the galaxy). Archer doesn't understand how Daniels can still exist with his timeline so radically changed. Daniels claims not to know, but is also reluctant to go into the details of temporal mechanics with a person from Archer's era.
 * Yet another time change not having erased Daniels in "Carpenter Street" was explained as the ripple not having hit his century yet, but would if Archer didn't stop it. San Dimas Time.
 * The episode "Year of Hell" has Voyager going up against a ship which attempts to solve the galaxy's problems by Ret-Gone-ing them--an individual, a ship, or an entire species at a time. Voyager's crew builds special armbands to protect them from the time ripples while they fight--and then
 * A similar phenomenon occurs when Dr. Crusher is trapped in a pocket universe in "Remember Me". As reality in the pocket universe keeps shifting so that there are fewer and fewer people on the ship, everyone but her remembers this as how things have always been. Eventually:


 * In Heroes, "Five Years Gone", Future Hiro remembers the timeline where Claire wasn't saved, but nobody else does.
 * Interestingly, because Claire's survival is kept a secret from Future Hiro, he doesn't notice a difference between the timeline in which Claire was killed and the one in which she wasn't. Because of this, it's debatable whether he has Ripple-Proof Memory or not - because there's no difference, we wouldn't know if he previous memory was overwritten as soon as he sent Peter to save Claire.
 * Rimmer and Holly display this ability in the Red Dwarf episode "Timeslides".
 * Further, in "Angels & Demons", Lister mentions having "played pool with planets" as a point of reference for the remarkability of his first taste of an edible pot noodle. However, according to Kryten's explanation at the end of "White Hole", he shouldn't have been able to remember that. But that's okay.
 * As Kryten himself admits on one of the Smeg-Ups blooper specials, he was originally programed to clean toilets, not explain things like DNA or time paradoxes. "In other words, I made a mistake. OK?!?"
 * He also says that no-one's ever seen a white hole before, so some of the theories about how they work (including not remembering things) might not be correct.
 * In Primeval series 2, Nick and Helen Cutter are the only ones who can remember.
 * Used in Mystery Science Theater 3000 episode 821 "Time Chasers". Crow, attempting to help Mike, goes back in time to keep him from getting stranded in space. When he returns, he learns that instead of Mike, he's partnered with his chain-smoking, beer-swilling Jerkass brother Eddie, who's whipped Servo into a quivering yes-man; only Crow remembers the original timeline, which he eventually restores.
 * In Terminator: The Sarah Connor Chronicles, the memories of time-travellers are apparently unaffected by timeline changes, as Derek Reese has flawless memories of meeting Andy Good in the future -- despite the fact that, after travelling back to The Present Day, he murdered Andy, and their meeting thus never happened.
 * It's pretty clear that everything in the Terminator universe has Ontological Inertia, including people; John Connor doesn't vanish when the Machine War is averted in T2, nor do his mother's memories of Reese change no matter how much the War gets moved around (for that matter, the Kyle that Derek remembers probably isn't the Kyle that Sarah slept with, what with perturbations in the time stream, but John's genes don't change). In that universe, once something happens or exists, that's that.
 * Considering that the War wasn't averted, Reese still time traveled to save Sarah and conceive John.
 * Yeah, but the Reese that sired John traveled from a future where the war started in 1997. If Reese had to go back again, in the new timeline, it'd be a Reese who saw the war start in 2011. Essentially, a different person -- conceivably, he could go back and find the grave of the earlier version of himself who died in the first movie.
 * This is easy: original Reese is from an alternate future, where the war began in 1997.
 * However, in at least one episode this is not the case: when Jesse kidnaps Charles Fisher from the future, she remembers Derek relating numerous tales of being tortured by Fisher, but Derek himself has no memory of any of that. They conclude that they are from two different futures.
 * Inconsistently subverted on Quantum Leap, where sometimes Sam remembers the unaltered timeline, and sometimes -- as in the case of one change that resulted in his earlier self marrying the girl that initially got away -- he doesn't. Some of this can be handwaved away with his "swiss cheese memory", but not all of it. The bulk of evidence suggests that if Sam's memory is changed at all, the changes only occur when he leaps. Al, however, always seems to remember the old timeline -- that is, if he hasn't been erased and replaced by Roddy MacDowell, at least. It helps that he has Ziggy.
 * In the episode "What Ever Happened to Sarah Jane" of The Sarah Jane Adventures, an alien artifact bestows this power on whoever holds it at the "time" of the Ripple Effect.
 * In one episode of the revived The Outer Limits, an already-unbalanced scientist uses her time machine to go back and execute notorious serial killers before they hurt anyone. Each time history changes, and she remembers each and every change, driving her crazier and crazier. In the end,
 * In the Time Cop TV series, one episode has Logan and a villain accidentally altering the timeline in such a way that when they get back to the future, Logan is now a criminal mastermind and the villain is still in good standing with the police force. The versions of the characters that were just replaced had their own ongoing schemes- but the Ripple Effect Proof versions don't have a clue what's going on. This leads to such increasingly circuitous bouts of Fridge Logic between everyone's interactions that the show becomes So Bad It's Good.
 * Angel, of the eponymous vampire-detective series, had an episode in which he dealt with the Oracles (Deus Ex Machina -- almost literally -- disciples of the Powers That Be) to have a day undone and so that he was the only one who had memory of the events.
 * Kamen Rider Ryuki: All Kamen Riders recruited by Shiro Kanzaki . Since Shinji just stumbled onto his card deck, this makes him immune.
 * Mostly averted in the second season of Witchblade. At the end of the first season, Pez . She doesn't retain any actual memories of the original timeline, but she does sometimes have a sense of when she should do something differently from the first time around, most notably.
 * In Kamen Rider Den-O, the Singularity Points like protagonist Ryotaro don't just have Ripple-Effect-Proof Memory, they have Ripple Effect Proof Existence, meaning that they can exist outside of time and changes to the timeline don't affect them at all; movie villain Gaoh needs an incredibly powerful MacGuffin just to kill Ryotaro and make it stick. This is a major plot point in several parts of the show, most prominently
 * In Smallville, Clark travels backwards in time at least three times (once with a Kryptonian Crystal to save Lana's life, once with the future Legion of Superheroes' ring to undo his revealing to the world, and once to save himself as a baby in Krypton), and always remembers the timelines that no longer exist. None is longer than a day or two, so it's not a big deal. Also, this is Superman, so he's pretty much Everything-proof.
 * In the lead up to the third example, Kara sent a message from past Krypton, which Dr Swan recieved in 1989 and recorded in his journal. Clark, reading the journal in 2007, notices the page is "new".
 * When Cole from Charmed changes the past, with the help of the Avatars, to ensure his conquering of Pheobe's heart (well not really), Paige "accidentally" sneezes in the middle of the ripple effect, ending up in the alternate present where everyone else forgot about her. They were actually aiming to remove her from continuity, and it technically worked, but her presence there
 * Parker, the hero from Seven Days, was picked by Project Backstep for his high tolerance for pain and a photographic memory. He would be briefed on the event that needed to be changed and sent back to change it.
 * Though neither he, not other characters from the series have Ripple-Effect-Proof Memory. It did happen to a kid where the alien spacecraft went through a plane, who could remember the past seven days. Parker on the other hand, if he's not the one piloting the machine, forgets like the rest of them.
 * The fourth season of Fringe

Tabletop Games

 * Feng Shui's Innerwalkers have this by default. Once someone has been through the Netherworld, they're basically removed from the timestream, and are thus unaffected by whatever changes are wrought by the chi of the world changing hands. They keep all the memories they have of what the world was like before entering the Netherworld, and thus do not have their memories changed like everyone else's when a shift happens. But the thing is, when something like a critical shift happens, the innerwalker can easily find himself as a much different version of himself from the new timeline, complete with a new name, new history, new enemies and the like, and no one who hasn't been through the Netherworld will remember anything but what the current version of the character is like, leading to serious Mind Screw.
 * A pretty good (and amusing) example is given in a supplement of two Innerwalkers who barely knew each other. A critical shift hits, and they find themselves world famous... and married. They're living together now, to keep up the celebrity mega-couple act, and are quite surprised to be slowly falling in love. The shift does suggest that if they had known each other, they'd get married, and they're sure getting to know each other now.
 * It's notable that some of the fluff fiction in supplements have characters changing equipment and abilities in a critical shift; a character with arcanowave schticks ending up without the implants and with different schticks after arcanowave tech is eliminated from the timestream, for instance, even though their memories remain. It contradicts the actual rules on what happens to Innerwalkers, but Feng Shui always does play a little fast and loose with rules.
 * Likewise, in the Zagreus arc of the Big Finish Doctor Who audios, the Neverpeople, Gallifreyan criminals sentenced to removal from history, retain their memories of the timeline that had been theirs, while the rest of the universe -- including the people responsible for their removal -- have no recollection of them. One strange side effect is that the Time Lords believe that this particular method of execution has not been used in eons, since, in the resulting timeline, its victims never existed in the first place. Of course, given how duplicitous Time Lords and their politics can get, and how evil the Neverpeople are, how much we can trust what we're told is arguable.
 * This also can be purchased as the advantage of Temporal Inertia in GURPS.
 * In the AD&D 2E supplement Chronomancers, time traveling characters are vulnerable to changes made to their past -- and aren't able to do much to prevent it, since they can't travel to a time they've already lived in. However, the supplement also includes a high-level spell that severs your personal time line, making it so you were immune to any changes made to your past, and so you could overlap your own past.
 * In Mage: The Ascension Czar Vargo (a powerful Steampunk Mad Scientist mage with a bit of an idealistic bent) attempted to prevent World War One with an unprecedented global display of the power of his technomagic. He pushed reality so far that when it snapped back it erased all memory of him from existence, and to this day the only knowledge of him comes from a tiny handful of eyewitnesses who retained their unedited memories of the event.
 * History in Genius: The Transgression has been accidentally changed in radical ways a few times despite the best efforts of various groups to preserve the timespace continuum, although neither the general population nor reality itself generally seem to notice. This means that some of the most spectacular world-changing events in the game setting only happened in continuities that no longer exist, and are only remembered by time travellers and a few other scattered people who somehow manage to remember them. As well as a few not so world-changing events, like each and every one of the successful Hitler assassinations.
 * The 1980's time travel game "Timemaster" used a version of this. When history is changed, everyone including the PCs remember the changed version ... but if the PCs make their "Paranormal Memory" roll, they also remember the original timeline.

Theatre

 * The above quote is from Rosencrantz and Guildenstern Are Dead, in which The Player, unlike the rest of the cast, remembers what's happened in each production of Hamlet, and thus knows what will happen.

Video Games

 * In Achron, you play a general precisely because of your nature as an 'achronal': an entity outside of time and unaffected by changes to the timestream.
 * Link (and Tatl) in The Legend of Zelda: Majora's Mask. Possibly the Happy Mask Salesman as well. Probably justified since the Goddess of Time is the one enabling them to travel back in time.
 * One of the most interesting aversions of this trope is the Journeyman Project games. The main character is a member of the titular Journeyman Project, a government agency which was created in response to the emergence of time travel technology to keep history from being changed. Changes in time create a temporal distortion that travels only forward in time from the moment of the change. One agent is constantly on duty to monitor for such changes; in the event that one occurs, the agent time-jumps back into the time of dinosaurs, a period of history considered "safe" because any changes would wipe out humanity. A record of all events in human history is kept there and can be referenced against a similar record in the future. The differences allow the agent to pinpoint the focal points and prevent the changes. The only reason this works is because the agent and lithmus record are not actually subjected to the ripple.
 * Only the first one, technically, although Ripple-Effect-Proof Memory is generally averted. In the later entries, it becomes possible to detect changes to the timeline without the archive disc. The latter is part of the backstory of The Journeyman Project 2: Buried in Time, where Gage Blackwood (the first game's unnamed Agent 5) is falsely accused of tampering with history for personal gain; the evidence against him consists of mini-temporal distortions originating from several time periods he visited. In the opening of the third game, Agent 3 tries to get the TSA's attention by leaving her Jump Suit time machine behind, setting off a massive temporal distortion.
 * Anyone in Time Hollow for the DS who either owns a Hollow Pen or was pulled through a Hole has this. Used as a bit of a running gag with one character who introduces himself to the main character every time they meet, since the main character meets him about once per chapter, and undoes their meeting at the end along with everything else that went wrong that day.
 * The main party in Chrono Trigger. Anyone that time-travels, for that matter. The fansite "Chrono Compendium" calls this phenomenon "Time-Traveller's Immunity", and extends it to include total immunity to any change that occurs due to their own travel. (Except, oddly, at the beginning of the game when Marle  But that seems to be the exception in the game, not the rule.)
 * The most commonly accepted theory is that it was done by The Entity in order to set the rest of the games events in motion. There's no Word of God on it though.
 * A weird related effect occurs in Mario & Luigi: Partners In Time. At one point, you end up altering E. Gadd's memories of the past. He's susceptible to this, but somehow realizes it's happening.
 * Montague Castanella of City of Heroes gets Ripple-Effect-Proof Memory as a superpower. He was already a proficient mage before he realized he had this ability; there wasn't a reason to suspect he possessed it until the Time Police showed up.
 * In Dark Cloud 2, Monica, the time-traveler from the future, naturally retains her memories of what said future should have been like until Griffon destroyed it from the past. As she and Max work together to restore the future (well, future from Max's perspective, but Monica's past) they run into a small bit of Time Travel Tense Trouble (for instance, they must create the origin of a factory that Monica remembers as having provided technology to a lab, even though neither the factory nor the lab exists yet.) As they restore these "origin points" and more elements from these locations reappear, inhabitants of restored future villages have no memory of what should have been there, but they do feel that "something is missing" until the village is completed. In the most notable case, a king from the future is astonished at a change in history he doesn't remember, but that Elena, his contemporary, recognizes it as an improvement Max and Monica made in the past's future known timeline (implying that she is aware of, and remembers, both the original and the improved one.) Meanwhile, their flunkies just roll with it, and presumably their memories were rewritten along with history.
 * And it goes without saying: although the Big Bad is defeated in the present (Max's time,) monumental events threaten the world and remains of the battle stay there (such as ) the good guys from the future have no knowledge of any this until it actually occurs.
 * Averted in CROSS†CHANNEL. Taichi and Youko often figure out what's going on, but that is because there is one spot that doesn't reset at the end of every week. Records of past Taichis are kept here. However, Nanaka DOES remember all the past weeks. But, as Taichi notices, she's not really 'there' and isn't exactly looping like the rest.
 * This comes with the Reality Warper abilities of the Star Singers in Final Fantasy Crystal Chronicles Ring of Fates. Of course it only applies to the one doing the altering at the time.
 * Averted in Legacy of Kain: Soul Reaver 2, where after a subtantial Time Paradox takes place, Kain is seen in clear anguish as new memories flood his mind, realizing that.
 * Not exactly averted. Kain still seemed to remember the original timeline, and that's what was causing his anguish and allowed him to give Raziel one last piece of advice to avert the change
 * Played straight in Singularity as Renko as well as everyone on the island is perfectly aware of what is happening to the timeline. This is what allows Barisov to attempt to fix the timeline.
 * Star Trek Online, being a veritable font of Continuity Nods, naturally ends up featuring this in some way. The most prominent example is likely the "Past Imperfect" storyline, which, as noted above, involves the Guardian of Forever granting Ripple Effect-proof memory to the player's crew due to proximity. There are also some unusual examples, in that  It also leads to some fairly amazing Tricked-Out Time, Stable Time Loop, etc. moments.
 * The fact that in Persona 2: Innocent Sin
 * This is a major character point to Rachel (and by proxy, her butler Valkenhayn) in Blaz Blue, who  It is also shown that   shares this ability in the second game.
 * It might also be a Deconstructed Trope, as it is heavily implied that Terumi, who has lived through FAR more loops than Rachel, eventually snapped and decided to pay the world back for every single loop he had been forced to relive in it.
 * Dissida states that the warriors are kept called for the next cycle of war - the side that lost will have no memories, though, while the winning warriors remember their last battle.
 * This happens to anyone Sissel helps in Ghost Trick (by way of going back in time and preventing deaths), himself included. Granted,

Web Comics

 * Explicitly "explained" with the retroactive changes caused by the Misfile: Ash and Emily can remember their lives before reality was changed because their souls are unavailable to the filing system for updates, so their memories can't be altered by the filing system. The other main character in on the secret, Rumisiel, is an angel, and so is either not included in the filing system or are unaffected by changes to Earth's files.
 * Rumisiel may not be ripple proof; he only knew that he'd messed up a couple of files and roughly where to find his victims. His first guess on what he'd done to Ash was that he'd aged her into a teenager.
 * Of course, it's entirely possible that he was too high at the time to realize exactly what he'd done, and only figured it out once he was explicitly told.
 * A great deal of the plot of the now-completed webcomic Narbonic is based on the time-travel adventure of Dave Davenport, and on the fact that afterwards.
 * Largely, this is an extremely long-term Foreshadowing of events involved in the series finale. Which happened years earlier in real world time.
 * This bites Zoe in the ass in Sluggy Freelance. She is downright pissed to discover that, thanks to the changes she made to the past, her history exam now includes an essay question on "The War of the Bug Squishers", a war Zoe helped start by going back in time, and consequently, doesn't know how it ended (or even that it's the same war she helped start).
 * Not involving actual time travel, but a teacher at the school The Good Witch is immune to the effects of the mass memory-altering spells that convince everyone else that the past happened differently.
 * Both played straight and double-subverted in Wapsi Square. Jin remembers every iteration of the Stable Time Loop the characters are meant to resolve, but isn't talking. Meanwhile, wrote a book  that explains step by step what to do, which is only accessible due to the existence of the Bibliothiki. The main character, however, is left completely in the dark until it's resolved.
 * For some unexplained reason, when history began to change in Ansem Retort, Riku had this. He managed to get Axel and Zexion to remember the proper timeline when he got them to remember that Andrew Jackson  is on the twenty dollar bill, and not Jack Bauer.
 * In Schlock Mercenary, when Kevyn Andreyasn and a miniature version of Sergeant Schlock went back in time to prevent the Bad Future, Schlock accidentally merged with Future!Schlock and now has both sets of memories.
 * In Homestuck, it's literally Dave's role as the Knight of Time to keep everyone from getting killed or losing the game by time traveling and warning his past self in the 'Alpha timeline.' And dooming his own timeline for his inevitable death.  So there logically follows there are many Daves running around at any given hour in time loops. And maybe a couple of dead Daves.

Web Original

 * Ben "Yahtzee" Croshaw's short story, Richard and Maureen's Amazing Time Travel Adventure plays with the trope. The main characters of the story are able to invent a time machine and make changes in the timeline merely by speculating about them. As they're doing this, their memories of how things used to be spontaneously vanish.
 * At the climax to Red vs. Blue's Blood Gulch Chronicles,
 * Has someone at RT read ? Just saying...

Western Animation

 * In Code Lyoko, the Return to the Past function doesn't affect the memories of anybody who has been scanned into the Supercomputer (as well as all the Supercomputer's programs -- and incidently XANA). However, they only travel to the past and see it as Mental Time Travel, which avoids some problems (most notably, they always remember both histories).
 * Lampshaded in an episode of Static Shock: A new metahuman with time travel powers who goes by the name of Timezone appears and teams up with Static and Gear; they, along with Ebon, have a time travelling adventure, at the end of which Timezone goes back in time and prevents herself from ever getting powers. She ends up with no memory of the events, and as Richie explains, their adventure now never happened. When Virgil protests that he and Richie both remember the events, Richie advises him not to think too hard about it.
 * American Dragon Jake Long lampshaded this in the last episode. Jake is talking about Rose, and Spud points out that Jake shouldn't even remember her because of how his wish altered reality. Jake presents a photo and Spud says that that shouldn't exist either.
 * In Justice League Unlimited, the League goes on a time-travelling adventure against Chronos; while several members travel around, only the two that are there when the reset happens remember it.
 * And those two (one of whom is Batman) have to take a moment to recover from the mental whiplash of cutting instantly from a desperate chase through time to... sitting calmly at a cafeteria table, back where it all started.
 * Earlier, in "The Savage Time," a force field that Green Lantern was using to guide a spaceship in for a landing protects him and everyone in it from the effects of a timeline change.
 * Jackie Chan Adventures had an episode in which the Big Bad Shendu had used Jackie in a plot to rewrite the history of the world (in a literal, giant Book of History) that more or less canceled all of Shendu's defeats and favors the villains. While in the process of rewriting history, Jade rips a page off the book that mentions her place in history. She keeps this paper so when history is rewritten only she remembers how things were. In this alternative reality Shendu also remembers what things were like, so he is surprised when Jade is able to gather all the main characters to combat him. In the end, the good guys rewrite history to what things were originally like and only they remember this alternative reality.
 * All humans retain their original memories in that series when history is altered by time-travel even the ones who didn't travel. For example, when Jade accidentally went back to 1976, she prevented Jackie from gaining a scar. While it disappeared from Present Jackie's body, he still remembered it and that clued him to the place in time she went to. When Future Jade came to Present Time to destroy a set of magical teeth so they wouldn't be used to restore Shendu, Future Jackie and Future Uncle still remembered them being used in their time.
 * Averted in Kim Possible: A Sitch in Time, where nobody remembers the alternate timeline at the end... except Ron has a subconscious aversion to Norwegian meatcakes, and can't figure out why.
 * Played straight earlier in the movie, where Ron is looking at yearbook pictures, and is confused when one of them changes.
 * In an episode of the Men in Black animated series, an enemy uses time travel to slowly reduce the MiB to a small backroom operation. Jay is the only one who notices the changes, as he had been previously affected by an alien device that made super-intelligent and immune to the ripple effect.
 * In Danny Phantom, Clockwork sets time back two hours before the Nasty Sauce incident that would trigger the Bad Future so neither Danny's parents nor his teacher Lancer gained knowledge of their once imminent deaths and Danny's Secret Identity.
 * Averted in the South Park episode "Go God Go XII". Cartman calls his past self, causing several changes to the future world that Cartman apparently doesn't notice.
 * In the episode of The Adventures of Sonic the Hedgehog where Robotnik, Scratch, Grounder, Sonic and Tails go back to an Ancient Egypt-like era, Scratch and Grounder make it so that two of Sonic's ancestors don't meet, resulting in Sonic not being born. But though Sonic disappears from existence, for plot convenience Tails is still there and remembers him, allowing him to set Sonic's ancestors back up.
 * In the Futurama episode Time Keeps On Slippin', everyone in the Universe has this for variable stretches of time. Looked at another way, it's a case of collective Laser-Guided Amnesia, where the laser is pointing at certain periods of time.
 * After Johnny Test changed Porkbelly's history, he had to take a test about the city's history. He failed it because he remembered the original history and not the new history.
 * Dog City: Baron goes back to the time the pilgrims purchased the new world from the natives and made a better offer: squeak toys. This created a Bad Future where he rules. Somehow, Ace and Eddie had Ripple-Effect-Proof Memory and, after visiting a timeline where Eddie ruled, went back to the past and made an even better offer: a technologically advanced (even for present time standards) fire hydrant the heroes took from the Eddie-ruled timeline.

Real Life

 * This help wanted ad.
 * Stephen Hawking's time traveler party, as mentioned in Into the Universe. No one came... or did they? Maybe he's keeping mum.
 * Nah, nobody wants to hang with Stephen Hawking.