The addition of people is _all_ the difference. :) You see, it's a different mode of performance. That's just how communication works - it engages us differently, and we have to engage other capacities than simply those that produce sound in the shape of words. Stutter variance has a lot to do with that - those factors that are external to our personal situation. Of course, internal factors matter too - like, how well did we sleep, are we nervous, stuff like that. So, if we sit around on our own and concentrate on speaking... that's not going to help us perform better in situations that differ a lot from that. And most of them do, since there where speech comes into play.