Letters 124.24

Only consider yourself happy when all your joys are born of reason, and when—having marked all the objects which men clutch at, or pray for, or watch over—you find nothing which you will desire; mind, I do not say prefer. Here is a short rule by which to measure yourself, and by the test of which you may feel that you have reached perfection: “You will come to your own when you shall understand that those whom the world calls fortunate are really the most unfortunate of all.” Farewell.

Seneca, Letters to Lucilius 124.24, translated by Richard Mott Gummere