Duties are universally measured by relations. Is anyone a father? If so, it is implied that the children should take care of him, submit to him in everything, patiently listen to his reproaches, his correction. But he is a bad father. Is your natural tie, then, to a good father? No, but to a father. Is a brother unjust? Well, keep your own situation toward him. Consider not what he does, but what you are to do to keep your own faculty of choice in a state conformable to nature. For another will not hurt you, unless you please. You will then be hurt when you consent to be hurt.
The chapter is often misread as enjoining unconditional obligation. It does not. Epictetus is clear elsewhere that you may protect yourself, and that submission to ongoing harm is no part of Stoic discipline. What the chapter insists on is that the relation is not under your control. Whether you are still in it — given the actual conduct of the other party — is, in the Stoic frame, more given than chosen. The duty is therefore set by the shape of the relation, not by the worthiness of the person standing in it. You consider not what they do but what you are to do. That asymmetry is the discipline.
Epictetus, Enchiridion 30 · trans. George Long (1877)
Context
One of the structural Stoic statements on relational duty — the chapter Epictetus uses to insist that a kathēkon (appropriate action) is fixed by the relation itself, not by the deserts of the other party. The doctrine is load-bearing for any case where the practitioner is asked: do I still owe this person anything? The Stoic answer is calibrated, not unconditional — the duty is real, the protective limits also real.