One of the things I do when I teach is to demonstrate painting techniques. Sometimes I already have a painting in mind and sketch it out before class, knowing it can work for a demo.
However, most of the time it is a technique or project that I start with the class or a demonstration of a technique for one of my student's projects. Then, I have a partial painting or just some random colors and texture that I can turn into something else.
Over the last couple of years of teaching, I have accumulated more unfinished pieces than I have managed to complete. I just counted 59 I had photgraphed last fall to record the process of painting. Rather daunting. I had no idea there were so many. Not all of them will be completed. For those that will be completed, something about them inspires me to press on with them.