If a man, says Epictetus, resists truths that are all too evident, in opposing him it is not easy to find an argument by which one may cause him to change his opinion. The reason for this is neither the man’s ability nor the teacher’s weakness; nay, when a man who has been trapped in an argument hardens to stone, how shall one any longer deal with him by argument?

Now there are two kinds of petrifaction: one is the petrifaction of the intellect, the other of the sense of shame, when a man stands in array, prepared neither to assent to manifest truths nor to leave the fighting line.