" If a man, said Epictetus, opposes evident truths, it is not easy to find arguments by which we shall make him change his opinion. But this does not arise either from the man's strength or the teacher's weakness; for when the man, though he has been confuted, is hardened like a stone, how shall we then be able to deal with him by argument? "

― Epictetus , A Selection from the Discourses of Epictetus with the Encheiridion