For me, a story idea is like a match. It can be very small, but with a lot of potential. I can light it and go looking for something to make a bigger fire of. Sometimes I'm walking in fog and there's nothing to burn, and the match goes out. Sometimes I find a worm-eaten library where I can immolate the words of centuries in a blaze so bright it makes the pages smoke. Usually it's something in the middle, but I never know until after I've lit the match and started looking.
I'd like to say it takes a lot of courage for me to write the way I do, but I don't think it does, for me. That's just what I do...trust my process and follow the headlights. But it might well take a lot of courage for you to write the way I do — light the tiny match and see where it goes.
I think the key "aha" here, at least potentially, is that the definition of what constitutes a viable story idea varies considerably from writer to writer. At one end of the spectrum, some people need a tight outline, character sheets, even charts and maps — they need to see the story before they set word to page. It's not an idea til its thoroughly worked out. At the other end of the spectrum, there's idiots like me bumping about in the dark, setting fire to our hair, failing a lot, but producing good work often enough that no one generally notices.
What does an idea look like to you?