Can’t Hurt Me by David Goggins is a memoir and self-improvement book about his transformation from a troubled childhood to becoming a decorated U.S. Armed Forces member and elite ultra-endurance athlete. It details his life of adversity, including poverty, abuse, and prejudice, and how he built mental toughness through discipline and self-challenge. The book argues that most people tap into only 40% of their capabilities, introducing the “40% rule” and encouraging readers to push past self-imposed limits to unlock their full potential.