This movie is a lot deeper than what it seems - Noah keeps going back in time to win over the woman he thought he was supposed to be with, despite clear signs that they were not destined to be together.
The moral of the story is truly moving, that no matter how much you wanted something; our stories are already written and fate (Kismet) is unfolding right before our eyes, that there is nothing we can do about it it rather than just accept it.
No matter how beautiful, heart-wrenching, sad or joyful the events in our lives are; that they were always supposed to happen and that we never have full control over the preordained and if we try to change it, that it will only fall back into what was meant to be each and every time.
(For example, in the movie; Ethan and Avery were always supposed to be together and later engaged, regardless of Noah trying to stop them from meeting in the first place. They would keep finding their way back to each other).
Noah ignored fate so the universe had to remind him by showing that when he did get what he wanted, other parts of his life weren’t whole or had completely been destroyed (some of his friendships, his ability to play piano, his authentic personality, his free time…etc).
Then when he started living his life the way it was always supposed to happen, he was able to keep everything he ever wanted and more.
That he didn’t have to compromise a part of himself or leave behind anyone/anything, the universe showed and was leading him what he NEEDED not what he wanted.