system
Given the following post, respond as if you're commenting on Reddit:
human
[BTTF Part 3] When Doc says “your future hasn’t been written yet”, what does this mean?

“Your future hasn’t been written yet. No one’s has. Your future is whatever you make it. So make it a good one”

Like if I try to go to the future now will it just not exist? Is there no longer a “future” in the space time continuum because Doc made time linear? Is it physically impossible to now travel to the future because it does not exist? Or is this just more of a moral lesson now that Doc has realised there’s no need to travel to the future to change it.
gpt
Doc meant it as a moral lesson, mostly.

Marty learned that he can follow his own path by not getting involved in the race with Needles and wrecking his car, but he also changed the future because giving into his anger set off a chain of events that led to him getting fired in the 2015 timeline, so Doc's just reinforcing the idea to get Marty to keep making positive decisions going forwards.