Enchiridion XXXVII

XXXVII

If you have assumed any character beyond your strength, you have both demeaned yourself ill in that and quitted one which you might have supported.

What is a character beyond your strength? It is a character that professes that it can determine events in the world outside the mind. This is a great human desire; even Aristotle falls prone to it in the later parts of the Nicomachean Ethics, in which he describes the virtue of courage as the virtue that wins wars. In the earlier parts he is more careful: virtues are to be judged by probability of outcome, and courage is said to be a virtue even though it is sometimes the very thing that destroys you. On average, however, courage works out with reasonable reliability. In the later books, he offers what philosophers sometimes describe as a 'thicker' version: courage wins wars, and thus wars are in a way a competition of virtue. The most virtuous in this particular way will be the winner.  

That is not true. The bravest does not always prevail. To assume a character that asserts that it is so courageous as to be undefeatable is to lie to one's self, and to those who believe you. Many a man has promised his wife and children to return from the war victorious, and then never returned at all. It was not because they were not brave men.

Epictetus suggests that lying to yourself is demeaning; and asserting a greater power than you have is a lie. A better man would not lie to himself, but would be honest about his limits as well as his powers. 

If you abandon that honest character in order to assert more boldly than you can really defend, then you are exactly as he describes in this chapter. You quit the honest character you could have defended, and demeaned yourself by lying. This is not virtue, neither courage nor any other.