The Enchiridion, by Epictetus.

The Meditations of Marcus Aurelius is studied and admired by successful people the world over. Marcus Aurelius thought of the Enchiridion in a similar fashion. This is not esoteric philosophy. The Enchiridion is a guide to developing an internal monologue that fosters determination, resilience, pragmatism, and an escape from the anxiety that grips so many in the modern world. 

The Enchiridion is a collection of Epictetus' lectures, written down and compiled by his student and historian Arrian of Nicomedia.

Translated by Thomas Wentworth Higginson.