Adjacent to the Problem

A comment elsewhere by Deep Lurker nailed something so fundamental that I don't think I'd ever fully realized it before, when brainstorming story ideas and rejecting what seem like perfectly reasonable suggestions:

When I have a Cool Idea as a story-starter, I really don’t want it to become the Story Problem. It might be the Cool Solution to the problem, but I don’t want it to be the problem itself, and I really don’t want “Something goes wrong with Cool Idea” to be the problem. Instead, I need something else adjacent to be the problem.

This isn't every story idea I get... but it's a lot of them.

For example, I have this idea for a novel about a war criminal who joins an FTL colonization ship in order to make a fresh start. That's an intriguing character and a good scenario, but it's not a plot. And the thing is, I don't want it to be the plot; doubtless his past will come out at some point, and it's certainly going to influence some events, but whatever the plot is (and I have no idea, yet), it's not about his past. It's about something else entirely; at most, something "adjacent".

I'm still processing how to incorporate this into my ongoing quest for plot discussion, but I wanted to get the concept down for reference.