Do you stutter when alone ? Why is there variability in stuttering behaviors if its neurological genetic disorder ?

Do you stutter when alone ? Why is there variability in stuttering behaviors if its neurological genetic disorder ? What causes us to stutter in public but most of us cease to stutter when alone ? Is it explained by some sort of excitation feedback which activates neurological defect ? Is stuttering a threshold condition ? What do you think cause for this is ?