"The principal act of fortitude is endurance, that is, to stand immovable in the midst of dangers rather than to attack them." - St. Thomas
"Fortitude and magnanimity. They are like the two opposite sides of a pointed arch, supporting each other.
Fortitude is the moral virtue which strengthens the soul in the pursuit of the difficult good so that it does not allow itself to be shaken by the greatest obstacles. It should dominate the fear of danger, fatigue, criticism, all that would paralyze our efforts toward the good. It prevents man from capitulating in a cowardly manner when he should fight; it also moderates audacity and untimely exaltation which would drive him to temerity.
Fortitude has two principal acts: to undertake courageously and to endure difficult things. The Christian should endure them for the love of God; it is more difficult to endure for a long time than in a moment of enthusiasm, to undertake courageously something difficult.
Fortitude is accompanied by patience to endure the sorrows of life without being disturbed and without murmuring, by longanimity which endures trials for a long time, and by constancy in good, which is opposed to obduracy in evil.
To the virtue of fortitude is also linked that of magnanimity, which leads to the lofty practice of all the virtues, avoiding pusillanimity and effeminacy, but without falling into presumption, vainglory, or ambition." - Garrigou-Lagrange