Can't Hurt Me — David Goggins (2018)

David Goggins's memoir-cum-self-help manifesto, describing his transformation from an abused, overweight, barely literate young man into a Navy SEAL, ultra-endurance athlete, and the only person to complete Army Ranger School, Navy SEAL training, and Air Force Tactical Air Controller training, has sold 5 million copies. Its principle of the "40% rule" — that when your mind tells you you're done, you're actually only at 40% of your capacity — has resonated powerfully with readers who reject the comfort-focused mainstream of self-improvement.