Here is the first page of Chapter 7 in Learn Faster, Perform Better by Molly Gebrian:
I'm so impressed by her empathy and professionalism. Dr. Molly does not blame the student for having feelings. What would be the point of making him feel bad for having normal student struggles? He cares about his progress, or why would he be taking lessons? Dr. Molly just rolls up her sleeves and teaches him different practice strategies so his playing shows improvement during the lessons.
Reading this book, I realized what my actual problem is. It's called "the illusion of mastery." Just because I can play well enough at home to get an "error free" recording, 1) doesn't mean it's a good recording, and 2) it doesn't mean I know the piece as well as I think I do! I find that fascinating! So Dr. Molly says the solution for this is changing the way I practice. As soon as a piece feels solid, she says it's time for "interleaved practice," to get it to performance standard.
I understand what people are saying here, that a lesson is not a performance. I get that. Certainly not every moment of a lesson is performance. I'm comfortable in the rest of the lesson, taking critical feedback, learning new things. Not a problem. I love receiving helpful notes on my pieces! It's a lot of fun, like doing a puzzle!
But on page 80, the good Dr. Molly says, "Now think about what a lesson often looks like: you have to perform your piece in front of your teacher (italics mine) without stopping, trying to get it right on the first try. That is a very different thing you are asking of your brain than when you were home practicing."
I feel SUPER RELIEVED that all I have to do is make some changes in how I'm practicing so I can learn the piece more thoroughly! Woohoo! Until I read this, I was actually convinced that the very fact that I played worse in lessons was some kind of indication that I have hit a ceiling and could go no further. Apparently, this is not at all what it means. It just means I have to change something, and I can TOTALLY DO THAT!