- What? What about my future?
- I can't tell you. It might make things worse.

7 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 01:08:32.826 in the DVD version of the movie.

Quote context

[...]

- Marty, why are you wearing that gun? You're not considering going up against Tannen tomorrow?

- 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.

- 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.

- What? What about my future?

- I can't tell you. It might make things worse.

- Wait a minute. Doc, what is wrong with my future?

- Marty, we all have to make decisions that affect the course of our lives.

- You've got to do what you've got to do, and I've got to do what I've got to do.

- Marty, I've made a decision. I'm not going with you tomorrow. I'm staying here.

[...]