I can't think of a decent thesis on Eternal Sunshine of the Spotless Mind.
To me it seems as if Clementine & Joel's destiny is to meet again, they are ready to give it a go again regardless of what they found out about each other. They knew each other before, it seems like destiny.
I think that with such a rich and intellectually complex film, some structure and guidance will be needed in helping to construct a thesis statement. If you have some type of assignment task present, it might allow you the chance to be able to structure what has to be included in your writing sample to ensure that you have some guidance. The film itself contains so many powerful and philosophically profound ideas that it is easy to become lost within them. Obviously, I think that memory and pain would be elements that can be incorporated in a thesis statement. Another topic to discuss would be whether or not there is such a thing as fate or destiny and how human freedom plays a role in such conceptions. I would also think that another topic to discuss is the role of ownership of shared memories and whether or not those could ever be erased.
I love this film! What a great question you have to do! Well, just a few suggestions to help you along then. I guess the crux of the film is about wiping out our memories. Can we really change our destiny if we forget about someone completely? The case in point is Kirsten Duntz's character, who ends up having another relationship with the Doctor, even though she has had her memories erased once. It appears that the message of the film is about the danger of playing with memory - we can't change our destiny it appears by erasing certain parts of our lives, and the film suggests it is actually dangerous to do so. Part of being human is coping with the pain and the hurt of events when we would rather forget they ever happened. Hope that helps!