>*"Why we don't stutter when we are alone and why we do stutter when with other people? "* I believe it's likely the same answer to the question, why don't we stutter when silent mouthing a word (aka without voice), but we start stuttering if we add voice. Both "*other people('s judgement)*" and "*our voice*" might be triggers, but I think they only trigger us when we have high expectation that make us intolerant for such triggers, whereby we have "learned" to blame such triggers or rely on reducing such triggers (resulting in abnormal dopamine release > cortico-BG loop dysfunction > disrupting speech initiation). If it's true that there are multiple types of speech blocks in developmental stuttering, then this might be one of them.