Letters 124.23

Are you not willing to abandon all these details—wherein you must acknowledge defeat, striving as you are for something that is not your own—and come back to the Good that is really yours?

And what is this Good? It is a clear and flawless mind, which rivals that of God, raised far above mortal concerns, and counting nothing of its own to be outside itself. You are a reasoning animal. What Good, then, lies within you? Perfect reason. Are you willing to develop this to its farthest limits—to its greatest degree of increase?

Seneca, Letters to Lucilius 124.23, translated by Richard Mott Gummere