From Wilderness at Sinai (#643) by Rabbi Avigdor Miller
Q: We know what’s right and wrong. Why do we need a chacham (sage) to teach us?
A: The answer is we don’t know. All you know in general you shouldn’t do it. The chacham will teach you the genus, how shameful it is what a harm that you do to yourself and that’s what the Mishlei is explaining constantly. The Sages say, what is Mishlei? What is mussar?,It’s learning how shameful it is to do wrong things.
Let’s say a man is a kaasan, an angry man. He thinks it’s wrong to be angry, it’s a sin to be angry, but he feels it shows a certain strength of character, and it’s some sort of an enjoyment. It is an expression of his will, it’s masculine to be angry. That man should know he’s very far away from being a baal teshuva (penitent person) on the middah (quality) of kaas.
He has to learn that anger is such a shameful thing that suppose he was walking in the street or he was in his office, or even his home and suddenly his pants fell down, whenever he recalls that episode, years later, his face flames with embarrassment. Now it wasn’t a sin, his belt burst and his pants fell down; it wasn’t his fault. But still whenever he recalls that, he’s terribly embarrassed. That’s how a man should think about his sin. He should learn how wrong it is, how shameful it is, and that's a baal teshuva.
And therefore that’s one of the requirements of teshuva, to lose any interest in the thing, to such an extent that when he thinks about it now, his heart hurts him that he ever did it.