Some painters work on twenty to thirty paintings at once, like Malcolm Liepke. I'm working on 12 paintings right now. Most are in my head and are composed and worked out. I will allow the process of these totally worked-out pieces to evolve and take me in a refinement direction but not a complete left turn to something totally different...that would be a different painting which I, of course, will make a note of for safekeeping.
I learned from songwriting to notate or record a demo of an idea quickly without critique to save it for another time to develop.