Jim taught physical conditioning to firefighters in New York City. He told me that sometimes recruits would enter the fire academy with massively sculptured bodies. But with no endurance. They would have trouble carrying a few shopping bags two blocks. Firefighters need to be able to wear and carry heavy equipment up many flights of stairs under adverse circumstances for extended periods of time.
Endurance is a prerequisite for perseverance.
Jim was a triathlete. He had also run numerous marathons, and some fifty miles races as well. Once a week, after mellowing out his body with a heavy workout in the gym, he would visit a hospital for paraplegics. It was there that Jim made a special friend. Roger was completely paralyzed, mute, and helpless.