Discourses, "What Things We Should Exchange for Other Things" (§1)

“Keep this thought in readiness, when you lose anything external, what you acquire in place of it; and if it be worth more, never say, I have had a loss; neither if you have got a horse in place of an ass, or an ox in place of a sheep, nor a good action in place of a bit of money, nor in place of idle talk such tranquillity as befits a man, nor in place of lewd talk if you have acquired modesty. If you remember this, you will always maintain your character such as it ought to be.”