What are the sins opposed to the virtue of fortitude?
They are, on the one hand, fear, which lacks courage in the presence of dangers of death, or insensibility to fear in the presence of peril, which is the lack of shunning peril when one ought to; and on the other hand, rashness which rushes towards danger imprudently (CXXV.-CXXVII.).
Can then one sin by excess of bravery?
One never sins by excess of bravery; but one may, under the impulse of excessive courage which is unrestrained by reason, be so carried away as to perform acts that are not really acts of true courage, but have only the semblance of bravery (CXXVII. 1, Obj. 2).
Next - The Catechism of the Summa - XLIII. OF THE VIRTUES ANNEXED TO FORTITUDE; OF MAGNANIMITY; OF THE SINS OPPOSED TO MAGNANIMITY; VIZ., OF PRESUMPTION; OF AMBITION; OF VAINGLORY; AND OF PUSILLANIMITY (A)