Doc: Marty, why are you wearing that gun? You're not considering going up against Tannen tomorrow?
Marty McFly: Doc, tomorrow morning, I'm going back to the future with you. But if Buford Tannen comes looking for trouble, I'm gonna be ready for him. You heard what that son of a bitch called me last night.
Doc: Marty, you can't go losing your judgment every time someone calls you a name. That's exactly what causes you to get into that accident in the future.
Marty McFly: What? What about my future?
Doc: I can't tell you. It might make things worse.
Marty McFly: Wait a minute, Doc. What is wrong with my future?
Doc: Marty, we all have to make decisions that affect the course of our lives. You've gotta do what you've gotta do. And I've gotta do what I've gotta do.