The Enchiridion (5-6)

Men are disturbed not by things, but by the views which they take of things. Thus death is nothing terrible, else it would have appeared so to Socrates. But the terror consists in our notion of death, that it is terrible. When, therefore, we are hindered, or disturbed, or grieved, let us never impute it to others, but to ourselves; that is, to our own views. It is the action of an uninstructed person to reproach others for his own misfortunes; of one entering upon instruction, to reproach himself; and of one perfectly instructed, to reproach neither others nor himself.

Be not elated at any excellence not your own. If a horse should be elated, and say, I am handsome, it might be endurable. But when you are elated, and say, I have a handsome horse, know that you are elated only on the merit of the horse. What then is your own? The use of the phenomena of existence. So that when you are in harmony with nature in this