Do you feel like your idea is really half-formed, or is it more half-buried? I ask because I find that when a story idea hits me, rare though that is, once I start unwinding it into actual words, it's all there. I'm not so much creating it as discovering what was there. But yes, finding out what happens as you go--that's my experience too.

I love the near-mystical-experience quality of it, but it's not a very businesslike or reliable method of actually getting much writing done. Maybe I'll never get to that.