Today it’s all about passion. Find your passion. Live passionately. Inspire the world with your passion. Passion, we tell ourselves, is the source of joy.

The Stoics disagreed. In fact, they believed that passion(s) were what contributed to our misery. To the experts and gurus who assure us that passion—that unbridled enthusiasm, that willingness to pounce on what’s in front of us with the full measure of our zeal—is our most important asset, Seneca would ask, “how can such wavering and unstable persons possess any good that is fixed and lasting?

So what should we pursue? Where do we find joy? And how do we keep it? Seneca’s answer comes in his letter, On the True Joy which Comes from Philosophy:

“It comes from a good conscience, from honorable purposes, from right actions, from contempt of the gifts of chance, from an even and calm way of living which treads but one path…There are only a few who control themselves and their affairs by a guiding purpose; the rest do not proceed; they are merely swept along, like objects afloat in a river. And of these objects, some are held back by sluggish waters and are transported gently; others are torn along by a more violent current; some, which are nearest the bank, are left there as the current slackens; and others are carried out to sea by the onrush of the stream. Therefore, we should decide what we wish, and abide by the decision.”

Unshakeable joy comes from purpose. In something bigger than yourself. In perspective and gratitude. In the wisdom that philosophy teaches us. It might not be as exciting or as glamorous. It might be a little slower. But it’s far more durable and meaningful.

Finding that will take time and work and self-reflection. But it’s in there. Inside you. Dig deep. Find it. And you’ll have joy you can hold onto forever.