The info is from a renowned slp. But it makes sense. A lot of struggle is due to the approach-avoidance conflict. You want to speak (approach ➡️) but you don't want to stutter (avoid ⬅️). What this looks like in action is, do this with your fists 🤜🤛. When the desire to speak is matched or exceeded by the fear of stuttering, you don't risk it, but since you still want to talk you'll open your mouth, try, but fear won't let you risk it so you block. If you give it enough time, often the fear will die down enough to where you can get it out. The approach-avoidance conflict applies to most if not all struggle behavior when stuttering not just blocking. It comes I believe from. Joe Sheehan https://www.mnsu.edu/comdis/kuster/pioneers/jsheehan/sheehanmem.html