To sim or not to sim?

There is this thing where the "what if's" go around and around in my head, usually as not much more than a dull roar in the background. What if this character had said this instead of that? What if over here this happened? And off they go playing out in detail somewhere on the edge of my consciousness. Every so often one of them will come to the forefront of my thoughts and I will scribble them down for further thinking about later. Sometimes though; this happens:

( processing the process )