- You're not gonna believe this.
- We gotta go back to 1955.
- I don't believe it.

Marty Mcfly (Michael J. Fox), Dr. Emmett Brown (Christopher Lloyd)

5 seconds sound clip from the Back to the Future Part II movie soundboard.

You can hear this line at 01:01:13.470 in the Blu-ray version of the movie.

Quote context

[...]

- I suppose it's poetic justice.

- Two McFlys with the same gun.

- Idiot.

- What the hell? (2)

- Nice shot, Doc!

- You're not gonna believe this.

- We gotta go back to 1955.

- I don't believe it.

- That's right, Doc. November 12, 1955.

- Unbelievable that Old Biff could've chosen that particular date.

- It could mean that that point in time inherently contains some sort of cosmic significance, almost as if it were the temporal junction point, for the entire space-time continuum. On the other hand, it could just be an amazing coincidence.

- Damn! Got to fix that thing.

[...]