Understand before you resent
Principle 42 from the Enchiridion
Understanding that does not excuse the harm, but it can change your response. People often act badly because the action looks right to them at the time.
Original Passage
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."
Modern Interpretation
According to Epictetus, people act on what seems right to them at the time, even when their judgment is mistaken.
Remembering that "it seemed right to them" creates room for a firm response without feeding hatred. Understanding how someone arrived at a harmful action does not mean approving it or allowing it to continue.
In Practice
A coworker unfairly criticizes your work in public. You feel the anger arrive immediately.
Remind yourself that their judgment looks correct to them right now. Then answer with facts, ask to continue the conversation privately, or set a clear boundary if needed.
Reflection Question
Who is frustrating you right now? If you remembered that their action came from their own judgment, would your response change?