Epictetus said (The Enchiridion, 1):
Some things are in our control and others not in our control.
Things in our control are opinion, pursuit, desire, dislike, and whatever are our own actions.
Things not in our control are body, property, reputation, politics, and whatever are not our own actions.
If you perceive that which is in your control to be your own, and that which belongs to others such as it really is, then no one will ever compel you or restrain you. You will not find fault with anyone. You won’t do anything against your will. No one will hurt you, you will have no enemies, and you not be harmed.
Work, therefore to be able to say to every harsh appearance, “You are but an appearance, and not absolutely the thing you appear to be.”
And then examine it by those rules which you have, and by this: whether it concerns the things which are in our own control, or those which are not; and, if it concerns anything not in our control, be prepared to say that it is nothing to you.