"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.