This is what I say: I've got good news and bad news. The good news is, you don't have to worry, you can't change the past. The bad news is, you don't have to worry, no matter how hard you try, you can't change the past. The universe just doesn't put up with that. We aren't important enough. No one is. Even in our own lives. We're not strong enough, willful enough, skilled enough in chronodiegetic manipulation to be able to just accidentally change the entire course of anything, even ourselves.