Not all pain is equal. As in anything else one learns the difference between discomfort and muscle fatigue/exhaustion and injury. I ran a half-marathon in fre

Not all pain is equal. As in anything else one learns the difference between discomfort and muscle fatigue/exhaustion and injury. I ran a half-marathon in freezing rain, and my feet started blistering badly about halfway. If I had been doing a marathon and my feet blistered that badly between 6 and 10, I probably would have dropped out, but it wasn't really bad until about mile 10, and I'd have had to have walked to the finish anyway, in freezing rain! Most elites will stop and accept a DNF (Did Not Finish) if they a are really injured, and most fitness/recreational runners get a good sense of when it's the mind and not the body really screaming quit. It's like getting your breath knocked out of you. It's scary as hell the first time, but it's not a heart attack. There's lots of good, sound research on endurance running: Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance Running to the Edge: A Band of Misfits and the Guru Who Unlocked the Secrets of Speed Natural Born Heroes: How a Daring Band of Misfits Mastered the Lost Secrets of Strength and Endurance Life Is a Marathon: A Memoir of Love and Endurance Finding Ultra: Rejecting Middle Age, Becoming One of the World's Fittest Men, and Discovering Myself As an example of how running has impacted, not a CEO, but an international award-winning novelist, short story writer, and essayist see: What I Talk About When I Talk About Running by Haruki Murakami. And, related to the topic in general, see: The Beauty of Discomfort: How What We Avoid Is What We Need Grit: The Power of Passion and Perseverance Resilience: Hard-Won Wisdom for Living a Better Life Mastery: The Keys to Success and Long-Term Fulfillment