When conductors train their orchestra for a particularly challenging bit in a concerto, they will arrive at a point where improvement slows down, but does it ever come to a halt?
First, the error margin is reduced. 100% accuracy is required. Hitting the wrong key or snare is never an option. Once accuracy is achieved, the musicians could stop claiming; we now know this passage and can play it well. Are they, though?
What about the tempo? Is it being played as fast as it should be? What about playing that tricky part under pressure or with sweaty fingers? Is the artistic interpretation genuine, or are they too liberal with creativity?
As a conductor of an orchestra, or the CEO of a company, there is always room for improvement. Thinking there isn’t is a form of misplaced arrogance, one that typically isn’t helpful.