What would happen if you went back in time and killed your grandfather before he had kids? Would you still exist? Probably not, because you'd never have been born.
Or would you exist, because you're a time traveler who's just really good at math?
Or maybe, just maybe, your grandfather had a twin brother who was just as awesome, so you're actually the twin who got time-traveled?
Or maybe, just maybe, time travel is just an excuse for you to get away from your in-laws.