You hypocrite, first take the log out of your own eye, and then you will see clearly to take the speck out of your brother's eye.
~ Matthew 7:5
Remember that, as I said, the right direction leads not only to peace but to knowledge. When a man is getting better he understands more and more clearly the evil that is still left in him. When a man is getting worse he understands his own badness less and less.
A moderately bad man knows he is not very good: a thoroughly bad man thinks he is all right.
This is common sense, really. You understand sleep when you are awake, not while you are sleeping. You can see mistakes in arithmetic when your mind is working properly: while you are making them you cannot see them. You can understand the nature of drunkenness when you are sober, not when you are drunk.
Good people know about both good and evil: bad people do not know about either.
Lord, let me see my shortcomings clearly. Amen.
~ C. S. Lewis, from “Mere Christianity”