This quote definitely says something about Marty's ambition… and it ain't good. No matter what his musical aspirations are, this is a clear indicator that, when it comes to academics, it couldn't hurt for him to buckle down. We're already beginning to see where his priorities are.
Marty: Yeah, I know if you put your mind to it, you can accomplish anything.
The sentiment is a good one, but Marty's tone when he delivers it is less than convincing. Basically, he's regurgitating a piece of advice he's heard over and over again, but it doesn't mean anything to him (at least not yet). As the movie goes on, however, and Marty does a lot of putting his mind to things he realizes how effective the practice can actually be. He even rubs off on his dad.
Marty: Check out that four by four. That is hot. Someday, Jennifer, someday. Wouldn't it be great to take that truck up to the lake? Throw a couple of sleeping bags in the back. Lie out under the stars.
Not every ambition has to be about something you want to accomplish career-wise. Marty sees in his mind's eye the perfect weekend, with the perfect girl, and envisioning things repeatedly can often help them come true. We've been trying the same trick for years with our lottery tickets.
Doc: It's taken me almost thirty years and my entire family fortune to realize the vision of that day.
Key bit of information here. "My entire family fortune." So Doc used to be rich… which explains the nice, big house and access to expensive lab equipment. But when we meet him: no family, and no fortune. He sacrificed everything to achieve his vision. Now that's some ambition right there.
Doc: That's right, twenty-five years into the future. I've always dreamed of seeing the future, looking beyond my years, seeing the progress of mankind. I'll also be able to see who wins the next twenty-five World Series.
Another piece of valuable insight here is revealed by the words "seeing the progress of mankind." That's the main reason Doc wants to go into the future. Not to look up old friends, or see if the Eiffel Tower is still standing. His life revolves around science—it's his love and his passion—and the only thing in the world he wants is to see progress.
Goldie: No sir, I'm gonna make something out of myself. I'm going to night school and one day I'm gonna be somebody.
One of the most ambitious young characters in the movie doesn't get much screen time. But we know Goldie follows through on his dream, because in 1985 he's up for re-election as mayor. At least someone got their act together.