I think what Glass misses in the grandparent post is that this analytical/critical ability is not innate, but acquired along with the performance skill, and at times the analytical ability gets ahead of the skill.

Many years ago, when I was in a youth choir and we were practicing a lot for a festival, I asked our director why we sounded worse at each practice. His explanation was that we actually sounded better, but that our analytical abilities developed even quicker than our singing skills.