Letters 76.17

If every good is in the soul, then whatever strengthens, uplifts, and enlarges the soul, is a good; virtue, however, does make the soul stronger, loftier, and larger. For all other things, which arouse our desires, depress the soul and weaken it, and when we think that they are uplifting the soul, they are merely puffing it up and cheating it with much emptiness. Therefore, that alone is good which will make the soul better.

Seneca, Letters to Lucilius 76.17, translated by Richard Mott Gummere