I really like the Packman-Anastasio three-factor model: There's the causal neural deficits in speech production, which can be modulated by your own actions (careful speech behavior), but also exacerbated by other triggers (stress, anxiety). Here's the link to their full paper: https://www.sciencedirect.com/science/article/pii/S0094730X12000642?via%3Dihub Or, put simply: The speech system of stutterers is liable to break down at anytime, and is more likely to break down in certain situations, and/or under stress