Except I don't understand how Marty missing the lightning strike (at least in part 1, before he returned again to 1955) would create a paradox.

I ordered the 4K set when it came out, but never actually opened. Finally got around to (re)watching part 1. As many times as I’ve seen the film it amazes me how I can discover something new. At least to me.

I always found it odd when the police man asks Dr for the permit for the weather equipment he said sure just one minute. Like, how did he have the forethought to get a permit?! In the next scene Marty is putting the letter in Dr’s coat - which is what I always paid attention to. However, if you look in the background you can see Dr has his wallet out and seems the bribing the officer! I have no clue if I just happened to notice this or if it’s because it was in 4K. Sorry if an old observation.

I need to get this on 4K too. Part 1 was great, of course. But I think I "Part 2" could be my favorite of the three.

Going back to the original 20+ year-old question that started this thread - why DID Marty have to go to 1885? Since the Doc of 1955 now knew how he would die, couldn't he take precautions to prevent it from happening? It wouldn't have been too different from when Marty slipped him the letter about the Lybians. Doc in 1885 even said he wished he paid off Tannen when he had the chance once Marty told him what will happen - so by doing that he could have prevented his own death.

Would have been a fairly dull part 3 though.

Sentimental attachment. The Doc Brown trapped in 1885 was the one Marty first met, developed a friendship with, perhaps even grew up with depending how many years they'd know each other. Since they originate from the same time-line, he likely considers that "the real Doc Brown", and doesn't want to see him die unavoidably.

Yeah, "My friend was murdered, but I have a time machine" is a pretty straightforward character motivation, if you ask me