1 Adam: So anyway, time travel: Myth confirmed!
2 Jamie: Wait a minute. I don't remember our future selves coming back in time to visit us when we were in college. Do you?
3 {beat}
4 Adam: Parallel universes: Myth confirmed!

One of the literary methods of dealing with the complexities inherent in time travel is to posit parallel universes, such that when you "go back in time" you actually end up in a different universe where history was the same up until the point where you arrived, but can diverge after that, since in your original timeline you never actually showed up in the past. In this way, you can "change history" in the sense that you can alter the development of the parallel universe, but you can't alter your own past in the universe you originally came from. This avoids all the messy paradoxes of killing your grandfather and so on. You might never be born in the parallel universe, but that's fine, because you are still born in the universe you came from.

But that's no fun at all.