Marshall B. Rosenberg (2004). “Teaching Children Compassionately: How Students and Teachers Can Succeed with Mutual Understanding”, p.31, PuddleDancer Press
"The Golden Sayings of Epictetus" by Epictetus, translated by Hastings Crossley, Vol. II, Part 2, The Harvard Classics. New York: P.F. Collier & Son, 1909.