Be discriminating about what images and ideas you permit into your mind. If you yourself don’t choose what thoughts and images you expose yourself to… - Epictetus

Any person capable of angering you becomes your master; he can anger you only when you permit yourself to be disturbed by him.

"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."
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Here are thieves and robbers and tribunals: and they that are called tyrants, who deem that they have after a fashion power over us, because of the miserable body and what appertains to it. Let us show them that they have power over none.