Agreed that's the problem. You block because you won't let yourself stutter. Blocking is a learned behavior. It's learned and reinforced so much that it becomes automatic. It can be unlearned though. As much as it doesn't feel like it, you are doing the blocking, it is not some cosmic force happening to you. You do it because you want to talk but you don't want to not stutter more, so you open your mouth to talk but then your body locks up the cords because it knows you're afraid to stutter.