The Discourses of Epictetus (1.5)

It is said that there are those who will oppose very evident truths, and yet it is not easy to find a reason which may persuade such an one to alter his opinion. This may arise neither from his own strength nor from the weakness of his teacher; but when a man becomes obstinate in error, reason cannot always reach him.

Now there are two sorts of obstinacy: the one, of the intellect; the other, of the will. A man may obstinately set himself not to assent to evident truths, nor to quit the defence of contradictions. We all dread a bodily paralysis, and would make use of every contrivance to avoid it; but none of us is troubled about a paralysis of the soul. And yet, indeed, even with regard to the soul, when a person is so affected as not to apprehend or understand anything, we think him in a sad condition; but where the emotions

Are you certain that you are awake? am not, replies such a person, for neither am I certain when in dreaming I appear to myself to be awake. Is there no difference, then, between these appearances? None. Shall I argue with this man any longer? For what steel or what caustic can I apply, to make him sensible of his paralysis? If he is sensible of it, and pretends not to be so, he is even worse than dead. He sees not his inconsistency, or, seeing it, holds to the wrong. He moves not, makes no progress; he rather falls back. His sense of shame is gone; his reasoning faculty is not gone, but brutalized. Shall I call this strength of mind? By no means,—unless we allow it to be such in the vilest debauchees publicly to speak and act out their worse impulses.