I was at my daughter’s high school music recital last night. The jazz band had good players in it, but they didn’t do very well. Because I used to play trumpet, my wife leaned over to me and asked if there was something wrong with the trumpet. I replied that it wasn’t the instrument, but the player lacked confidence and that’s what she was hearing.
This article talks about why we choke under pressure, and what you can do about it. The book is going on my reading list.