DIOGENES used to say, "Ever since Antisthenes made me free, I have ceased to be a slave." How did he make him free? Hear what he says. “He taught me what was my own, and what not. An estate is not my own. Kindred, domestics, friends, reputation, familiar places, manner of life, all belong to another."
"What is your own, then?"
"The use of the appearances of things. He showed me that I have this, not subject to restraint or compulsion; no one can hinder or force me to use them any otherwise than I please. Who, then, after this, hath any power over me? Philip, or Alexander, or Perdiccas, or the Persian king? Whence should they have it? For he that is to be subdued by man must, long before, be subdued by things. He, therefore, of whom neither pleasure nor pain, nor fame nor riches, can get the better, and who is able, whenever he thinks fit, to throw away his whole body with contempt, and depart, whose slave can he ever be?"
EPICTETUS. DISCOURSES. Book iii. 23, 4.