There are two ways people harden themselves. First, they shut down their ability to think clearly. Second, they kill their sense of shame — they decide they won't accept obvious truths and they won't stop arguing. Most of us fear physical pain and will do anything to avoid it. But we don't care about damaging our souls. Here's the strange part: if someone can't think or understand anything, we say they're in bad shape. But if someone kills their sense of shame and decency, we actually call that strength.
Now there are two kinds of hardening, one of the understanding, the other of the sense of shame, when a man is resolved not to assent to what is manifest nor to desist from contradictions. Most of us are afraid of mortification of the body, and would contrive all means to avoid such a thing, but we care not about the soul's mortification. And indeed with regard to the soul, if a man be in such a state as not to apprehend anything, or understand at all, we think that he is in a bad condition; but if the sense of shame and modesty are deadened, this we call even power (or strength).