David Goggins, 44, is the only member of the U.S. armed forces ever to complete training as a Navy SEAL, Army Ranger and Air Force Tactical Air Controller.

He is also a former Guinness World Record holder for completing 4,030 pull-ups in 17 hours, and one of the world's top endurance athletes, having competed in more than 60 ultra-marathons, triathlons and ultra-triathlons. Recently, the retired SEAL became the New York Times best-selling author of "Can't Hurt Me."