Philosophy and Film

Back to the Future was an impossible story.
If Marty McFly went back to 1955 and rearranged how his parents met, being a more heroic, tumultuous tale, changing the outlook and esteem of his parents and context of 1985, we can assume that Marty's knowledge and upbringing would change as his story in their lives unfolded. In the "original" story, George McFly fell from a tree and was hit by Lorraine's dad, and she nursed him back to health, falling for him the whole way. Marty had heard this story his entire life. If this event changed, by, say Marty keeping George out of the tree in the first place, Marty's knowledge of the event that was "supposed" to happen, wouldn't exist. As the movie goes, the "original" story doesn't happen, so he shouldn't logically have any recollection of that story, so he wouldn't regret saving George from the car. At minimum consequence, he should have grown up with the story of a strange life-preserver wearing boy interrupting the couple's lives and changing HOW they met. The how is emphasized because we know some offspring of George and Lorraine existed in 1955 alongside them, then they met, they married, they had the child. But this is merely an unnecessary control. If Marty had changed the past so drastically that he wouldn't have been born (like killing his father), then he wouldn't just fade away in a curiously dramatic way, but he wouldn't make it to 1955, or exist at all to begin with. If Marty sees that he is conscious/alive/existing in 1955, then he can rest well knowing that his parents met and received each other. There would be no exact point of goofy disappearance.
David Lewis in Paradoxes of Time Travel points out that  an "original" story and a "new" one are one and the same. Marty cannot isolate himself from his context. The more he does in 1955 concerning George and Lorraine's story about how they met, and therefore are supposed to meet, the more Marty's memory about the story about how they met changes. As soon as Marty jumped out in front of the car to save George, that event has been told to him by his mother his whole life. He would have no recollection of the "original" story because, now, it never happened. To even say "as soon as" is irrelevant. Everything he does has already happened, so he comes into every event playing the roles that have already happened. Whatever memories he has must play out, further making the previous statement irrelevant. To come into 1955 as the 17 year old, rebellious, Van Halen loving teen we see, he would to only be able to watch. He is forced into being a ghost. To be Marty McFly at all, he cannot affect a past where he is not alive. If he goes back to 1980, for example, he can exist and manipulate his context, but only as a 12 year old normally would, blissfully unaware that he had just erased seven years of humanity.To put another way, Marty could be in the 17 year old inaffective ghost state until the second he was conceived, where he could begin to affect his context starting as a pupa.
It made sense in my head.