Part of me knows I usually start a story knowing the gist of it, and then sometimes I wing it, but I'm struggling right now because what I'm working on is a time travel story, and since I was small, I always believed the geniuses who write time travel stories knew every little nuance and paradox that was going to happen, and intended them all, when the fact is that there's no such thing as a totally succinct time travel story. Most of them can be hole-punched into Swiss cheese by asking questions that begin with "But wouldn't that mean ..." And unfortunately a lot of the time, I'm that guy. The one who didn't like Chrono Cross, but played through it over a half-dozen times trying to make sense of the time travel/parallel worlds in detail.
So my problem is shutting off that little nitpicking asshole part of my brain.