“[Human nature’s] natural inclination to virtue is diminished by sin because human acts produce an inclination to like acts. Now from the very fact that a thing becomes inclined to one of two contraries, its inclination to the other contrary must needs be diminished. Wherefore as sin is opposed to virtue, from the very fact that a man sins, there results a diminution of the good of [human] nature, which is the inclination to virtue.”  -St. Thomas Aquinas