5 Fear is not a just excuse for those who accept the challenge of a duel. They are afraid that they will be publicly disgraced as cowards if they refuse. Now if the duties of mankind are measured by the false opinions of the multitude, not by the eternal norms of rectitude and justice, there would be no natural distinction between honorable actions and disgraceful deeds. The pagan philosophers themselves both knew and taught that the fallacious judgments of the masses must be spurned by a courageous and steadfast man. It is rather a just and holy fear which prevents a man from committing murder and makes him solicitous of his own safety and that of his brothers. Truly, he who disdains the worthless judgments of the mob, who prefers to undergo the scourging of insults rather than abandon duty in any matter, proves himself to be of a far greater and exalted spirit than he who rushes to arms when provoked by an affront. Yes, indeed, if he wants to be judged rightly, he is the one in whom solid virtue shines forth. The fortitude is truly called virtue, and its companion is a glory, that is neither counterfeit nor deceptive. Virtue in a good man exists in accordance with reason, and unless virtue rests on the judgment of God's approval, all glory is vain.
Source: Pastoralis Officii (Vatican.va)