Epictetus, Golden Sayings 67

If I show you that you lack just what is most important and necessary to happiness, that hitherto your attention has been bestowed on everything rather than that which claims it most, and, to crown all, that you know neither what God nor Man is, neither what Good or Evil is; why, that you are ignorant of everything else, perhaps you may bear to be told.

But to hear that you know nothing of yourself, how could you submit to that? How could you stand your ground and suffer that to be proved? Clearly not at all. You instantly turn away in wrath. 

Yet what harm have I done to you? Unless indeed the mirror harms the ill-favored man by showing him to himself just as he is; unless the physician can be thought to insult his patient, when he tells him: 

"Friend, do you suppose there is nothing wrong with you? why, you have a fever. Eat nothing today, and drink only water." 

Yet no one says, "What an insufferable insult!" Whereas if you say to a man, "Your desires are inflamed, your instincts of rejection are weak and low, your aims are inconsistent, your impulses are not in harmony with Nature, your opinions are rash and false," he forthwith goes away and complains that you have insulted him.