Siena Katariina kirjast paavst Gregorius XI:
Oh, sweet and true knowledge, which dost carry with thee the knife of hate, and dost stretch out the hand of holy desire, to draw forth and kill with this hate the worm of self-love—a worm that spoils and gnaws the root of our tree so that it cannot bear any fruit of life, but dries up, and its verdure lasts not! For if a man loves himself, perverse pride, head and source of every ill, lives in him, whatever his rank may be, prelate or subject. If he is lover of himself alone—that is, if he loves himself for his own sake and not for God—he cannot do other than ill, and all virtue is dead in him. Such a one is like a woman who brings forth her sons dead.