Jennifer: Excuse me, Doc Brown. I brought this message back from the future and, well, now it's erased.
Doc: Of course it's erased.
Jennifer: But what does that mean?
Doc: It means your futures haven't been written yet. No one's has. Your future is what ever you make. So make it a good one, the both of you.
Doc: And in the future, we don't need horses. We have motorized carriages called automobiles.
Saloon Old Timer: If everybody's got one of these auto-whatsits, does anybody walk or run anymore?
Doc: Of course we run. But for recreation. For fun.
Saloon Old Timer: Run for fun? What the hell kind of fun is that?
Young Doc: All you have to do is drive the time vehicle directly toward that screen accelerating to 88 miles an hour.
Marty McFly: Wait a minute, Doc. If I drive straight towards the screen, I'm gonna crash into those Indians.
Young Doc: Marty, you're not thinking fourth dimensionally. You'll instantly be transported back into 1885, and those Indians won't even be there.