"In spite of the fact that Socrates studied with all diligence to acquire a knowledge of human nature and to understand himself, and in spite of the fame accorded him through the centuries as one who beyond all other men had an insight into the human heart, he has himself admitted that the reason for his shrinking from reflection upon the nature of such beings as Pegasus and the Gorgons was that he, the life-long student of human nature, had not yet been able to make up his mind whether he was a stranger monster than Typhon, or a creature of a gentler and simpler sort, partaking of something divine (Phaedrus, 229 E). This seems to be a paradox. However, one should not think slightingly of the paradoxical; for the paradox is the source of the thinker’s passion, and the thinker without a paradox is like a lover without feeling: a paltry mediocrity. But the highest pitch of every passion is always to will its own downfall; and so it is also the supreme passion of the Reason to seek a collision, though this collision must in one way or another prove its undoing. The supreme paradox of all thought is the attempt to discover something that thought cannot think."
From "The Absolute Paradox: A Metaphysical Crotchet," Chapter 3 of Philosophical Fragments by Søren Kierkegaard, trans. by David Swenson. Text via religion-online.org.