Yes, expectation is another factor. On a related but slightly different example, if I expect to stutter on a word or phrase, then I will. It's like knowing I'm going to have difficulty saying it. All I can do then is over a period of time, practice saying that phrase over and over when I'm alone, mindful of how it sounds, how it feels in my lips, throat etc. and after a while I know I can say it, thus changing my expectation. But I can only really do this if I've dealt with the emotional impact that stuttering used to have, and that's another factor.