There is an old story of the "Monster Study", where kids at an orphanage were basically (traumatically) told they weren't speaking correctly regardless of their speech fluency. Many seemed to develop a stutter. Great harm was done to these kids and it lead to major changes in research ethics as a result. The study has since been debunked somewhat; it seems the kids didn't acquire stuttering at all, but were majorly scarred. There is an undeniable emotional component to stuttering, but there isn't much good evidence that a traumatic event makes people stutter. Instead, it seems like childhood is hard on lots of people, including those with a genetic predisposition to stutter, so sometimes correlation is linked with causation. E.g., a parent reporting that they "caused" their child's stutter because they startled them one day and the child cried, and seemed to stutter after that. Humans look for patterns and there are so many rough spots in childhood that it's easy to point to one as the cause. I don't love the "trauma causes stuttering" hypothesis because it can lead to blame for what's ultimately part of normal human variation, but not everyone agrees with me, and we still live in a shitty world where people get mocked and degraded for sounding different.