Letters 9.19

There is a brave and stout-hearted man for you! The enemy conquered, but Stilbo conquered his conqueror. “I have lost nothing!” Aye, he forced Demetrius to wonder whether he himself had conquered after all. “My goods are all all with me!” In other words, he deemed nothing that might be taken from him to be a good.

We marvel at certain animals because they can pass through fire and suffer no bodily harm; but how much more marvellous is a man who has marched forth unhurt and unscathed through fire and sword and devastation! Do you understand now how much easier it is to conquer a whole tribe than to conquer one man? This saying of Stilbo makes common ground with Stoicism; the Stoic also can carry his goods unimpaired through cities that have been burned to ashes; for he is self-sufficient. Such are the bounds which he sets to his own happiness.

Seneca, Letters to Lucilius 9.19, translated by Richard Mott Gummere