By that point, the student knows he is in love with his craft, but is not yet certain it will reciprocate. Of course this is not the highest rank he could achieve, but such emphasis is placed on it, especially in American culture, that it almost seems like a test for adulthood, the dividing line between those who are worthy and those who are not. In the martial arts scale, the brown belt is like a teenager, given many of the responsibilities of an adult, but few of the rewards. Complicating this for the brown belts I am acquainted with is the fact that they are teenagers, with all the confusion that is common to the age. Brown belts are seldom given the luxury of concentrating on their own skills.
Brown belts do.
To the high-ranking instructor, some basics of the art are so basic that he doesn't even think about them anymore. Sometimes it's easy for him to assume that his students already know them, or in a large class, to not notice an individual student slipping up. Brown belts still remember how difficult the seemingly simple things were to master when they were first starting, and they serve as extra pairs of eyes for the instructor. I have long since lost count of the helpful suggestions they have offered for mastering techniques. I have yet to meet a brown belt who would abuse his position or his skill.