noun
rash courage; reckless bravery; foolhardiness
A classical expression for thoughtless, brute courage without wisdom or strategy. Often used critically or in contrast to true bravery. Rare in modern conversation but appears in literary or historical contexts.
それは匹夫の勇に過ぎず、真の勇気とは言えない。
That is nothing more than rash courage; it cannot be called true bravery.
猪突猛進 describes rushing headlong with reckless energy, similar in spirit but more vivid and action-oriented.
From classical Chinese; 匹夫 (a single man, an ordinary fellow) + の + 勇 (courage). The phrase implies the thoughtless bravery of an untrained individual.