Writing a story starts out as a puzzle in your mind, of "What is it I'm fantasizing about right now that makes me think this is going to be worth years of work?" And you just keep pushing and trying to figure it out, and once you've hit on these resonances... Then as a screenwriter, it can be dangerous if you get too hooked on just finding things that resonate with each other, because then you risk getting into stuff that's too neat, and becomes stifled as storytelling. But you do feel like you're on the right track when you start to have a sense of what goes with what.