Epictetus Enchiridion and Cebes Tabula (1660)

...you will indeed attain, on account of the desire for those things we mentioned before; but you will certainly fail entirely in those things through which alone happiness and freedom are acquired.

Chapter V.

Therefore, with every harsh impression, you shall immediately practice responding in this way: "You are an impression, and not at all the thing you appear to be." Afterward, in examining it, apply those rules which you have, and this one first and foremost: whether that impression concerns matters subject to our power, or indeed those belonging to others. If it concerns things outside of our power, have this response ready: "It is nothing to you."