On Anger, Book 3, Section 40 — In Plain English

Seneca — The Senator

There are two types of angry people, and you need different approaches for each. To the first type, say: "Don't let your anger give your enemies what they want." To the second type, say: "Don't let anger damage your reputation for being strong and level-headed. I'm honestly outraged by how you've been treated, and it breaks my heart. But we need to wait for the right moment. He will pay for what he did — you can count on that. When the time comes, you'll get him back with interest." Never scold someone when they're angry. That just makes you angry too, which makes them angrier. You need to approach them gently and go along with them — unless you have enough power to simply crush their anger. That's what Emperor Augustus did when he was dining with Vedius Pollio. One of the slaves broke a crystal cup. Vedius ordered the slave killed — and not just killed, but thrown to the giant eels he kept in a tank.

Seneca — The Senator Original

To one class of men you will say, “Beware, lest your anger give pleasure to your foes:” to the other, “Beware lest your greatness of mind and the reputation it bears among most people for strength become impaired. I myself, by Hercules, am scandalized at your treatment and am grieved beyond measure, but we must wait for a proper opportunity. He shall pay for what he has done; be well assured of that: when you are able you shall return it to him with interest.” To reprove a man when he is angry is to add to his anger by being angry oneself. You should approach him in different ways and in a compliant fashion, unless perchance you be so great a personage that you can quash his anger, as the Emperor Augustus did when he was dining with Vedius Pollio.[15] One of the slaves had broken a crystal goblet of his: Vedius ordered him to be led away to die, and that too in no common fashion: he ordered him to be thrown to feed the muraenae, some of which fish, of great size, he kept in a tank.