I feel like confidence plays a role because of my experience (anecdotal I know) I'm a shy guy and I tend to fear people's opinion about me. I don't have social anxiety but I'm definitely in the introvert sides. I stutter a lot, and it's mainly because I fear that people will judge me if I do something wrong. You can guess that I don't have the best relationship with my father. It's no the main cause but it definitely plays a huge part in its execution. My theory is that if I could be ultra confident (god mode), I would hardly stutter. Ofc every stutter is different, but if you feel like you're shy, it might be a good news because it's easier to become more confident than fluent.