A vice opposed to the virtue of fortitude by way of excess. Fortitude, or courage, moderates the passions or emotions of fear and daring; it is concerned with threatening evils that are difficult either to endure or to overcome. Fortitude has two functions: it strengthens a man to the endurance of an evil or to an attack upon it, depending upon which of the alternatives is judged reasonable. Foolhardiness is opposed to fortitude by facing danger and attacking when true virtue would choose rather to flee or to endure the evil. Not only does foolhardiness attack unnecessarily and unreasonably, but it is also likely to attack with greater violence than is warranted by the circumstances. Foolhardiness may be caused by presumption, as when one overestimates his own powers to repel evil (cf. Summa theologiae 2a2ae, 127.2 ad 1); by anger, which can lead to an attempt to repel an aggressor with unnecessary violence or to punish him; or by vainglory, for an attack against evil may come from an unreasonable desire to assert one's own will and gain esteem. It can arise from a contempt for life or for other goods that are risked, or from other causes.
Foolhardiness—like the other offenses against fortitude—is sinful, but its gravity depends on its causes and its effects. If temerity or foolhardiness leads one to put some great good in serious jeopardy or inflict grave harm unnecessarily, the sin is a grave one.
Bibliography: thomas aquinas, Summa theologiae 2a2ae, q. 127.
"Foolhardiness." New Catholic Encyclopedia. . Encyclopedia.com. (August 19, 2018). http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/foolhardiness
"Foolhardiness." New Catholic Encyclopedia. . Retrieved August 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/foolhardiness