Perseverance

If an unusual necessity forces us onward, a surprising thing occurs. The fatigue gets worse up to a certain point, then, gradually or suddenly, it passes away and we are fresher than before! We have evidently tapped a new level of energy. There may be layer after layer of this experience, a third and a fourth wind. We find amounts of ease and power that we never dreamed ourselves to own, sources of strength habitually not taxed, because habitually we never push through the obstruction of fatigue.

- William James (1842 - 1910) Psychologist and philosopher