It cannot be said that any of my teachers have students that play 100% perfectly 100% of the time.
So why do I worry so much about playing poorly, out-of-tune, with icky tone or strange musical sense? This afternoon I was practicing a piece, trying to play parts of it from memory and all of it nicely. It wasn't working out so well, and I was forgetting stuff and missing notes and screwing up with the bow. I kept imagining the teacher sitting there thinking "yep, there's an out of tune note, oh there's a wobbly-bow sound...now there should have been a crescendo there, where was it..." And even worse, I imagined playing it for my regular teacher in response to the inevitable what-did-you-do-with-your-summer and having him sit there and enumerate all the mistakes in his head. But really, do they do that? And if they do that, is there some kind of tipping point after which they go "god, I can't stand to listen to this shit one more minute, it's so bad"? Maybe, but if only perfect people took music lessons there wouldn't be too many musicians around. So anyway, this is something I just want to get over. I'm sure it's an "adult student" affliction.