- It means your future hasn't been written yet. No one's has. Your future is whatever you make it. So make it a good one, both of you.
- We will, Doc!

Dr. Emmett Brown (Christopher Lloyd)

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

You can hear this line at 01:50:39.981 in the DVD version of the movie.

Quote context

[...]

- You can't keep a good scientist down. After all, I had to come back for Einstein.

- And, well, I didn't want you to be worried about me.

- Oh! I brought you a little souvenir.

- It's great, Doc. Thanks.

- Dr. Brown, I brought this note back from the future, and now it's erased.

- Of course it's erased.

- But what does that mean?

- It means your future hasn't been written yet. No one's has. Your future is whatever you make it. So make it a good one, both of you.

- We will, Doc!

- Stand back! All right, boys, buckle up!

- Hey, Doc, where are you going now? Back to the future?

- No, already been there.

[...]