Question: Why does Doc suddenly change his ideas (about time travel and not learning too much of your own future) in Part 2? In Part 1, he was determined not to learn too much about his own future, despite Marty trying to warn him that his life depended on it. But in Part 2, suddenly it's okay to bring Marty to the future and give him enough information to try to change the course of destiny for his son. Also, wouldn't it have just been easier to warn Marty about the accident he was going to have that caused his life to go so wrong to begin with? One would have to think that if Marty becomes successful and lives out an entirely different life, then maybe his son doesn't turn into such a wimp.
unicorngoddess
24th Jul 2010
Chosen answer: Marty's saving his life with the note made him realize that some events are worth tampering with. He wasn't aware that Marty's entire life had taken a wrong turn, he'd just read that his son goes to prison after the robbery and takes action on that one thing.
Captain Defenestrator
The problem is that Marty becomes stupid when someone calls him chicken. So if Doc had just told him about the accident, well, maybe the accident would have been prevented. But then Needles would later goad him into doing something else stupid or damaging. Marty needed to learn the lesson for himself.