I’ve seen some videos of William Perry before👍. I would say you’re partially correct that I may always be at least slightly running a script of fear of speaking. But I really think that being deep in thought or even a little in thought about something unrelated to the current social situation contributes to stuttering. What I believe is happening is that your brain is trying to justify speaking something to another human being. But at the same time, if you are deep in thought and not mindful of the present moment, it’s like you are time traveling mentally to another place. So in that case, your mind is also believing that the present moment isn’t even a real thing; so it shuts down your speaking mechanisms. This doesn’t happen when we are alone, but I believe fear + disassociation from present moment creates more stuttering than with just fear alone. Though fear could often be described as disassociation anyways.