5. Why Don't Marty's Parents Remember Him From When They Were In High School? - Back To The Future
The "Plot Hole"
Back To The Future centres around teenager, Marty McFly, who accidentally travels back in time, stops his parents from meeting, and must get them back together before he's erased from existence. To do this, he teams up with hair-brained inventor and genius Doc Emmet L. Brown, and makes friend with both his future mother and father.
Eventually, he successfully reunites them as a couple. Back in the present, everything is returned to normal, with one glaring omission: why don't George and Lorraine McFly remember Marty from the past?
The Simple Solution
People really take this one to heart, as if there's enough evidence here to cite this as a genuine plot hole. But think about it for a second, and there are some simple reasons as to why they don't remember Marty being around in 1955 (and why they almost definitely wouldn't anyway). Firstly, they met him 30 years ago, when he "looked" 16 years old, on and off for, like, a week. How well do you remember somebody you met even 10 years ago for that length of time?
If you saw them 30 years later, would you really make such a connection? Nope. Secondly, the fact that the McFlys will eventually raise Marty as a child would remove any possibility that they'd associate him with "that kid who came and went from 1955." They'd see him everyday, after all, and he wouldn't look like 1955 Marty until he reached his teenager years anyway.
After all that time watching him grow up, they'd see him in a completely different light - from a baby to a toddler to a kid to a teenager. Their view of Marty would be entirely distorted. Thirdly, put yourself in their shoes: can you really remember the face of that kid who came to your school for a week and left again? I definitely can't, and there were a ton of them.