[jonnathanson]

"Not necessarily a pity. You have to be an expert at some things in order to become a beginner at others."

True, but I don't think that's the point of the passage. Rather, the idea is not to seal one's mind off at the "expert" level in any field of endeavor. At that point, we replace questions with assumptions. Those assumptions might be based on knowledge, and they might be right (for now). But who's to say that they're going to be right tomorrow? Or the next day? Or that a better way won't emerge? (It definitely will not emerge from the one who assumes he's mastered it, because he won't question what he assumes he's mastered).