According to the great Doctor of the Church, St. Thomas Aquinas, the virtue of humility consists in keeping oneself within one's bounds -- not reaching out to things that are above one, but instead submitting to one's superior. At the same time, excessive humility is as much a vice as pride, since servility might be derogatory to a man's office or holy character. Excessive humility might also occasion the sins of tyranny, arbitrariness, and arrogance in another.
The 1895 cartoon from Punch by George du Maurier facetiously entitled "True Humility" illustrates the point. A timid Anglican curate is taking breakfast at the home of his bishop. The bishop says, "I'm afraid you've got a bad egg, Mr. Jones." The curate replies, "Oh, no, my Lord, I assure you that parts of it are excellent!"
Sources: The Catholic Encyclopedia; Wikipedia
