At this point Montaigne is developing–whether after the fact with the constant editing or on-the-fly–a kind of exploratory, short-long rhythm in which a long piece is often followed by one or more short pieces that expand upon and/or temper what he has just written. In this case, having made a rather persuasive case for man’s power over all that most vexes and ails him, Montaigne observes that there are limits: mindless, obstinate defense that is pursued without reason (despite observations of the enemy one is facing) is useless and can be punished even with death. Courage and valor are one thing, haughtiness and foolhardiness quite another.
Stoicism is not a mindless philosophy, no matter how far-fetched some of the contentions might seem to those who don’t believe that man has such power over his own life, thoughts, and feelings. Ideally we can maintain control of ourselves and our perceptions even in the worst possible circumstances, but better not to find ourself in such extremes if we can help it (without being cowardly) and certainly better not to put ourselves into such situations for reasons of vanity or foolhardiness!