Memento

Because Leonard cannot remember what has happened in the short term, not only does he lose grasp of how time works, but he also gets out of step with his own identity. Unable to accumulate experiences, he becomes a kind of neutral identity, someone who could be anyone at any moment because he doesn't remember who he was just moments before. At one point, he switches clothes with Jimmy Grantz and takes Jimmy Grantz's car—but later he has no way of knowing that he has done so.