Malcolm Fraser! This quote is on page 145 of his book on self-help for stuttering. I read it years ago and it's stuck with me, it's a great analogy! https://www.stutteringhelp.org/Portals/English/book0012\_11th\_ed.pdf >But if that same plank is placed on a wall high above the ground, then, if asked to walk along the plank, he would probably develop a fear of falling. As a result, it would be difficult for him to walk along the plank in a normal way. In fact he would probably put on a poor exhibition of walking normally or “fluently.” This example is somewhat parallel to the problem of stuttering. Nearly all stutterers have the physical equipment to talk properly, but in many cases the fear of stuttering causes them to try to force trouble-free speech. And since it is difficult to force the articulative mechanism of speech, he does not speak fluently.