Yeah this is very common I believe. Also when people are in crowded places that can't hear their own voice, they don't stutter either. I believe there are some devices that try to replicate that to stop stuttering. Also if someone simultaneously says what you want to say and you know it, like if both agree to say "hello" at the same time, you won't stutter. At least I've heard this many times. It's kinda crazy lol