EPICTETUS. DISCOURSES. Book ii. §26. ¶1.
EVERY error in life implies a contradiction: for, since he who errs doth not mean to err, but to be in the right, it is evident that he acts contrary to his meaning. What doth a thief mean ? His own interest. If, then, thieving be against his interest, he acts contrary to his own meaning. Now every rational soul is naturally averse to self-contradiction: but so long as anyone is ignorant that it is a contradiction, nothing restrains him from acting contradictorily: but whenever he discovers it, he must as necessarily renounce and avoid it, as anyone must dissent from a falsehood whenever he perceives it to be a falsehood: but while this doth not appear, he assents to it as to a truth.