Caleb Ontiveros is the founder of Stoa, an app that combines the ancient philosophy of stoicism with mindfulness and meditation. He writes The Stoa Letter, co-hosts the podcast Stoa Conversations, and is the editor of The Classical Futurist. Caleb and I talk about the philosophy of Stoicism and what Stoics have to say about psychology, mental health, and human flourishing. We discuss Stoic conceptions of virtue, emotion, and self-control; similarities between Stoicism, System 1 and System 2 thinking, and cognitive behavioral therapy; and why Stoic thinkers and practices appeal so much to men. We conclude by speculating about whether today’s “meaning crisis” has always been with us, and whether material progress undermines opportunities to be virtuous.