From Fearless Creating by Eric Maisel, Ph.D.:
Naming the reasons why you are presently not creating will not help you change, any more than naming the safety features of an airplane will help a phobic person fly. The solution isn't in naming the excuses but in doing what cognitive therapists call "desensitization through successive approximations." This translates as "growing less fearful by taking baby steps."
The author recommends minuscule exercises. For artists, he says to just squeeze a dab of paint and study it. Don't paint a picture...yet.
Novelists just need to write one sentence.
Screenwriter: Do not start your screenplay. Just picture one scene. Picture it for a few seconds, then let it go. That's all. End of exercise.
I can do that. Even when stuck, or blocked, I can take a small baby step.