Epictetus on Argument

Epictetus, The Handbook, Section 42:

When any person harms you, or speaks badly of you, remember that he acts or speaks from a supposition of its being his duty. Now, it is not possible that he should follow what appears right to you, but what appears so to himself. Therefore, if he judges from a wrong appearance, he is the person hurt, since he too is the person deceived. For if anyone should suppose a true proposition to be false, the proposition is not hurt, but he who is deceived about it. Setting out then, from these principles, you will meekly bear a person who reviles you, for you will say upon every occasion, "It seemed so to him."