Note that '''You Already Changed the Past''' implies [[Only One Possible Future]], which is the version of [[You Can't Fight Fate|fatalism]] found in many [[Older Than Feudalism|older]] works, such as Greek Drama, that don't involve time travel.
This trope ''arguably'' makes the most sense when considering time travel from a scientific point of view, see the [[wikipedia:Novikov self-consistency principle|]] on [[wikipedia:Novikov self-consistency principle|The Other Wiki]].<ref>Novikov's self-consistency principle was named "the [[Law of Conservation of History]]" by [[Larry Niven]] in his short piece "The Theory and Practice of Time Travel," published at least ten years prior to Novikov's work. Of course, [[Larry Niven]] is a [[Science Fiction]] writer, which may explain why [[Sci Fi Ghetto|nobody cares]]. Alternatively, this is an illustration of something called [[wikipedia:Stigler's law of eponymy|Stigler's Law of Eponymy]]: nothing ever gets named after the first person to discover it.</ref> However, the number of time-travel plots that it allows for are extremely limited and the logic gets complicated ''very'' quickly. This, however, also has the side-effect of creating a '[[Functional Magic|self-correcting universe]]' usually by a slew of [[Contrived Coincidence]]s (ie. if you try to shoot your grandfather the gun will jam; if you try poisoning him he will recover; if you try strangling him you will be overcome; if you wear [[Power Armor]] from the future you will have second thoughts; if you try [[Beyond the Impossible|sending a bomb back through time and detonating it directly inside his chest]] the time machine will break down). This can also lead to a scenario where the ''only'' reason why the past is not changed is because someone else says 'you cannot' and you take his advice. Meaning ''the advice itself'' is a part of the universe's self-correcting nature.
Thus, most time travel stories that involve altering the past will provide some of the characters with [[Ripple-Effect-Proof Memory]]. This makes less sense, but it makes for a narrative convenience. If a You Already Changed The Past plot is used, the time travel will probably be a one-off thing, since repeating it would most likely get tedious.