"Can't repeat the past? Why of course you can!" How does the novel prove this statement to be true or false??
It seems as if Gatsby is trying to do exactly what your question refers to. He is trying to undo everything that has happened between his past romance with Daisy and the present situation. The fact that the novel ends tragically seems to show that you cannot repeat the past. Gatsby is an incurable romantic. He thinks that love conquers all, and that his love is so strong that he can actually conquer time itself. But Daisy is married. She has children. She has a whole social network built around her marriage. She herself is not an impractical romantic like Gatsby--although she might have been when she was young. She may find him attractive because of his bold character, but she wants comfort and security, not adventure and uncertainty. She must realize that Gatsby's castle is built on a very insecure foundation. Nobody--except Gatsby--knows where his money is coming from. Nobody comes to his funeral because he has no real social connections or even any real friends except possibly for Nick. Her present husband Tom may be unfaithful and have a lot of other shortcomings, including a dull mind, but he is a polo player with solid social connections. It might be argued that the story is not about Gatsby versus Tom but about Gatsby versus time. This makes him seem like a Don Quixote.