The Discourses of Epictetus, tr. by P.E Matheson, , at sacred-texts.com
If a man, says Epictetus, objects to what is manifestly clear, it is not easy to find an argument against him, whereby one shall change his mind. And this is not because of his power, nor because of the weakness of him that is instructing him; but, when a man, worsted in argument, becomes hardened like a stone, how can one reason with him any more?
Now there are two ways in which a man may be thus hardened: one when his reasoning faculty is petrified, and the other when his moral sense is petrified, and he sets himself deliberately not to assent to manifest arguments, and not to abandon what conflicts with them. Now most of us fear the deadening of the body and would take all possible means to avoid such a calamity, yet we take no heed of the deadening of the mind and the spirit. When the mind itself is in such a state that a man can follow nothing and understand nothing, we do indeed think that he is in a bad condition; yet, if a man's sense of shame and self-respect is deadened, we even go so far as to call him 'a strong man'.
Do you comprehend that you are awake?
'No,' he says, 'no more than I comprehend it, when I seem to be awake in my dreams.'
Is there no difference then between the one sort of impression and the other?
Can I argue with him any longer? What fire or sword, I say, am I to bring to bear on him, to prove that his mind is deadened? He has sensation and pretends that he has not; he is worse than the dead. One man does not see the battle; he is ill off. This other sees it but stirs not, nor advances; his state is still more wretched. His sense of shame and self-respect is cut out of him, and his reasoning faculty, though not cut away, is brutalized. Am I to call this 'strength'? Heaven forbid, unless I call it 'strength' in those who sin against nature, that makes them do and say in public whatever occurs to their fancy.