Stan Lee's Laziness Led to the X-Men
The hardest part of coming up with a new superhero is the origin story. You can't just have a guy in spider-themed pajamas shooting webs out of his palms with no explanation -- that would be ridiculous. There has to be this whole elaborate (and often grossly implausible) backstory about how he became who he is. And you have to put some thought into it, because you just know there will eventually be six or seven movie reboots covering that exact part of the story.
"Let's go realistic and gloomy for this one. Third time's a charm."
Well, the Patron Saint of Comics, Stan Lee, was all too aware of this when he was trying to develop a new team of heroes back in the early 1960s. How in the hell do you come up with a story for every one of these "X-Men" characters that explains how they all got different powers at once? So Lee said, and this is the actual quote:
"What if they were just born that way? Everybody knows there are mutations in real life. There are frogs that are born with five legs and so forth. I can get these guys to have any power I want. I'll just say, 'Well, they're mutants. They were born that way.' Nobody can argue with that!"
Sadly, Lee didn't go on to create Five-Legged Frog Man, but this is how we got basically all of the X-Men: characters with insane powers who have them just ... because.
The spirit of not trying would live on in every X-movie.
From there, it was easy -- Angel got his wings because Marvel hadn't made a character who could fly yet; Iceman came about because Lee wanted a second Human Torch, so he built a power based on the opposite of fire. And to quote the man on Marvel Girl: "I hated the name Marvel Girl, but I couldn't think of anything better." OK, maybe it's better sometimes to not know how your favorite things are made.