Sometimes when I'm watching/reading/playing something, I'll come across a plot point/character/setting/event that's really interesting. But then the game/movie/book does something different with it than what I was originally thinking. So, then I start to think about how I would have used that instead. That's where a lot of my inspiration comes from, seeing other people's work and then thinking about how I would have handled certain things, or taking an element from another's work and then spinning an entire story around it.
At its most basic, I'm stealing other people's ideas and using them in a way that's more interesting to me personally.
I mean, I once wrote a 1000-page scifi epic that inspired by the location used in a single episode of TV series that I liked.