Most of your bad days are filed under the wrong department
A Roman-era teacher born into slavery drew one line that, if you actually followed it, would eliminate most of your suffering.
Epictetus began his most famous teaching with a filing system, not a sermon. Everything that happens to you, he said, sorts into exactly two piles: things within your power, and things outside it. In the first pile: your judgments, your choices, how you respond. In the second: your body, your reputation, other people, the weather, whether the boat sails on time.
He was blunt about how much of daily misery comes from filing things in the wrong pile. You don't control whether the wind blows west. You control whether you spend the afternoon in the harbor, glaring at the sky, demanding it change its mind.
What makes this more than a productivity tip is where Epictetus put it: he had been enslaved for years before he taught philosophy in Rome. The dichotomy of control wasn't abstract for him — it was the difference between a man who owns your body and a man who owns nothing that actually matters about you.
He wasn't telling people to stop caring. He was telling them to stop wasting their one department on someone else's weather.