Why don't I stutter when feeling confident or if I know that no one's judging me?

Why don't I stutter when feeling confident or if I know that no one's judging me? For context. I'm 19M, finished high school. when I hit 11, I began to stutter suddenly. i had never stuttered before that time what's going on ? normally my brain saying all the right words and my mouth isn't cooperating, but this all goes out of the window if I'm confident or feel no one's judging me