Mastery. There are different levels of mastery, to be sure. There are virtuosi who can play anything at any speed without visible or audible effort. Not all of them have mastery. I have heard some who have no control over speed, for example. Because they can play anything their muscles run away, out of control.

Mastery--in the sense of full possession of one's own hand and one's own ear--is fully within the grasp of every musical person, even young children. My goal as a teacher is to acquaint each student with their own personal version of it. Nothing less.