The Stoic Way by Peter H. Samson.

"'The unreflective person thinks of himself as an independent unit in this world, complete in himself. His own private good is the criterion for every choice he has to make. But true wisdom begins when the individual reckons himself a fragment, a part of a perfect whole, the universe. He is under obligation to make the reason at the heart of things his own standard of behavior.'" - Zeno.