A large pile of research on various groups of people, covering various skill sets, indicates that in the face of all evidence, humans are irredeemably optimistic about their own abilities. That is, by itself, not such a bad thing. The ugly side shows up when we also realize that the norm must be maintained. Studies show that we do this by considering that everyone else is much worse. Being clueless about your own abilities is one thing. Misjudging others' abilities is relatively more serious.
Accurate self-assessment is a good thing in its place, but it seems almost the opposite of virtuous to be preoccupied with assessing oneself. The person who is constantly asking, "How am I doing?" "How do I measure up?" "How do I rank?" "What am I worth?" is too centered on his or her own value to count as humble in a virtuous sense. Humility, then, on this model, is a non-preoccupation or unconcern about one's rank and status and worth, but not an ignorance of it.
A management system known as "stack ranking" -- a program that forces every unit to declare a certain percentage of employees as top performers, good performers, average, and poor -- effectively crippled Microsoft's ability to innovate.