Discourses, Against the Quarrelsome and Ferocious

Epictetus — The Slave

Everything else in the world can be destroyed or stolen. If you get attached to these things, you're bound to be upset. You'll worry, you'll cry when you lose them, you won't get what you want, and you'll end up with what you're trying to avoid. So why don't we choose to secure the only real safety we have? Why don't we stop clinging to things that can be lost or taken away? Why don't we work on the things that last forever and are naturally free? Remember this: no one can actually hurt you or help you. It's your opinions about what happens that hurt you. Your opinions are what knock you down. This is where the real fight is. This is where the real conflict happens. This is war.

Epictetus — The Slave Original

All (other) things everywhere are perishable, easily taken by assault, and if any man in any way is attached to them, he must be disturbed, except what is bad, he must fear, lament, find his desires disappointed, and fall into things which he would avoid. Then do we not choose to make secure the only means of safety which are offered to us, and do we not choose to withdraw ourselves from that which is perishable and servile and to labor at the things which are imperishable and by nature free; and do we not remember that no man either hurts another or does good to another, but that a man's opinions about each thing, is that which hurts him, is that which overturns him; this is fighting, this is civil discord, this is war?