Instead of focusing on whether specific stimuli trigger stuttering, I'd say we should go deeper into the underlying mechanism. In the sense of, what mechanism did we develop that decides whether we speak our thoughts out loud or not - you can call it a protection mechanism or whatnot but the point is that everyone has different stimuli that leads to a trigger or panic response resulting in stuttering.. basically it varies from person to person. So, instead of asking: What psychological/environmental stimuli trigger our stuttering? Perhaps a more effective way to approach it, is by investigating how this mechanism works (that decides whether we release speech plans for overt execution) which has eventually led us to maintain a vicious cycle, and by investigating how you can break the vicious cycle of this mechanism. So, basically what I'm saying is, even if we are more confident in certain situations, we would still perceive "being unconfident" as a problem (or rather a speech error) and to be avoided.. in other words, it didn't lead us to decreasing this protection mechanism.. it's still there running in the background in our mind if that makes sense this is just my own take on it