An arrogant person considers himself perfect. This is the chief harm of arrogance. It interferes with a person's main task in life—becoming a better person.
When a person is haughty, he distances himself from other people and thereby deprives himself of one of life's biggest pleasures—open, joyful communication with everyone.
It is often better for a person to recognize a sin than to do a good deed. Recognizing a sin makes a person humble. Doing a good deed often can feed a person's pride.