On Anger, Book 2, Section 28 — In Plain English

Seneca — The Senator

We see other people's flaws clearly, but we're blind to our own. That's why a father who's worse than his son will criticize the boy for throwing expensive parties. He'll condemn any hint of luxury in others, even though he never set limits on his own indulgences. That's why tyrants get angry at murderers, and temple robbers punish thieves. Most people aren't angry at sins themselves — they're angry at the sinners. We'd be more reasonable if we looked at ourselves first and asked: Have I ever done something like this? Have I made this same mistake? Does it really benefit me to condemn this behavior?

Seneca — The Senator Original

We have other men's vices before our eyes, and our own behind our backs: hence it is that a father, who is worse than his son, blames the latter for giving extravagant feasts,[10] and disapproves of the least sign of luxury in another, although he was wont to set no bounds to it in his own case; hence it is that despots are angry with homicides, and thefts are punished by those who despoil temples. A great part of mankind is not angry with sins, but with sinners. Regard to our own selves[11] will make us more moderate, if we inquire of ourselves:—have we ever committed any crime of this sort? have we ever fallen into this kind of error? is it for our interest that we should condemn this conduct?