The Enchiridion;

The Enchiridion is a short manual of Stoic ethical advice compiled by Arrian, a 2nd-century disciple of the Greek philosopher Epictetus. For many centuries, the Enchiridion maintained its authority both with Christians and Pagans. Eschewing metaphysics, Arrian focused his attention on Epictetus's work applying philosophy in daily life: “What upsets people is not things themselves but their judgments about the things.” - Epictetus