From Rohan Healey's Greeks to Geeks: Practical Stoicism for the 21st Century
"The Self Esteem Trap
. . .
Epictetus: 'The things in our control are by their nature free, unrestrained, and unhindered; but those not in our control are weak, slavish, restrained, belonging to others. Remember, then, that if you suppose that things which are slavish by nature are also free, and that what belongs to others is your own, then you will be hindered. You will lament, you will be disturbed, and you will find fault both with gods and men. But if you suppose that only to be your own which is your own, and what belongs to others such as it really is, then no one will ever compel you or restrain you. Further, you will find fault with no one or accuse no one. You will do nothing against your will. No one will hurt you, you will have no enemies, and you will not be harmed."
Healey, using Epictetus, here examines how little importance a Stoic should place on things outside the control one's own control. He quotes Dr. Albert Ellis, founder of Rational Emotive Behavior Therapy (who based it on Stoic philosophical concepts), as saying "Self-esteem is the greatest sickness known to man or woman because it's conditional." Healey explains, "If you place your sense of value as a human being, your sense of self-worth, on something that lies outside your control, you are asking for trouble. If your sense of self-love relies on outside conditions you are giving away all of your power."
So what is self-esteem? Healey says, "True self-esteem is the confidence you gain when you know what is actually within your power, and by mastering and utilizing this knowledge." True self - esteem, then, is based on what is in our control - opinion, pursuit, desire, and aversion - the "Ruling Faculty" of Epictetus. This Ruling Faculty "is simply our ability to form opinions, to have beliefs, to reminisce about the past and to project into the future."