People don't usually stutter when they talk to themselves. It is possible to stutter when you talk to yourself when you are imagining you're talking to someone, but if you focus and you are aware that nobody hears you except yourself, it is extremely unlikely that you will stutter. Stutter is both psychological and physical disorder. I had some kind of an "experiment" with a colleague of mine - we had an online conversation and every time I started to stutter I muted myself on the app, and then I won't stutter. But immediately when I unmuted myself, I started to stutter again - it's because I was aware someone was listening to me - and therefore I felt the pressure of speaking fluently or being judged/bullied/misunderstood,...