Yes, yes, we're all annoyed as hell by the trend of prequels because everyone has to know everything about a movie's lore.
Seriously, who really cares about the Death Star being built? It's there floating in space, the construction of it doesn't matter, does it?
You also have to wonder why can't people come up with their own theories and ideas for movies, but even I can be this way myself if a movie is vague or doesn't answer certain questions.
Still, for some movies, we want to learn everything we can, and I stumbled across a fun one recently: How Doc Brown and Marty McFly first met up.
Frankly, I originally thought Doc was some kooky teacher in Marty's high school who got too kooky to hold down his day gig. But since the question was posed to Back to the Future screenwriter Bob Gale on Cinema Blend, I was curious to read his response to this. (Blend also brought up a good point, "What's a high school slacker doing hanging out with a weird scientist, anyway?")
A lot of times, actors and screenwriters will create backstories for characters that never show up in the actual film, but it's so they can give more depth and background to the characters they're playing or writing. As Gale told Blend, "For years, Marty was told Doc Brown was dangerous, a crackpot, a lunatic," and he had to find out why, as many young kids love to try something they're warned not to do.
"Marty then snuck into Doc's lab, and was mesmerized by all the cool stuff the good doctor invented. Then Doc and Marty met, and Doc was delighted to find that Marty thought he was cool and accepted him for what he was. Both of them were the black sheep in their respective environments."
Then Doc lets Marty come by and help out in the lab as a part time gig, which one days leads up to that magical ride in the DeLorean.
So that's how Doc and Marty came together and made a great cinematic team, and it's nothing that's going to spoil your experience watching the film.
But of course, please feel free to come up with your own backstory if you wish. That's part of the magic of going to the movies, is you don't always need all your questions answered, and you're more than free to add on to the story in your mind.