The Discourses of Epictetus, tr. by P.E Matheson, , at sacred-texts.com
Every error implies conflict; for since he who errs does not wish to go wrong but to go right, plainly he is not doing what he wishes. For what does the thief wish to do? What is to his interest. If then thieving is against his interest, he is not doing what he wishes. But every rational soul by nature dislikes conflict; and so, as long as a man does not understand that he is in conflict, there is nothing to prevent him from doing conflicting acts, but, whenever he understands, strong necessity makes him abandon the conflict and avoid it, just as bitter necessity makes a
man renounce a falsehood when he discovers it, though as long as he has not this impression he assents to it as true.
He then who can show to each man the conflict which causes his error, and can clearly bring home to him how he fails to do what he wishes and does what he does not wish, is powerful in argument and strong to encourage and convict. For if one shows this, a man will retire from his error of himself; but as long as you do not succeed in showing this, you need not wonder if he persists in his error, for he acts because he has an impression that he is right. That is why Socrates too, relying on this faculty, said, 'I am not wont to produce any other witness to support what I say, but am content with him to whom I am talking on each occasion; it is his vote that I take, his evidence that I call, and his sole word suffices instead of all.' For Socrates knew what moves the rational soul, and that it will incline to what moves it, whether it wishes to or not. Show the conflict to the rational Governing Principle and it will desist. If you do not show it, blame yourself rather than him who refuses to obey.