I think it's a big part of stuttering is habit, the same way we panic before speaking is a habit which in turn makes us stutter which re-enforces that we stutter, then we add secondary behaviours like others here have said. I pretty much lost my sever stutter in a week by breaking the habit but there's one word I still have trouble with "Diana" for some reason, this is a habit because I know I'll struggle with "Diana" so in turn, I struggle with "Diana".