Our greatest talent, he explained, also created the monster that could destroy us. “Unlike any other organism in history, humans have a mind-body conflict: we have a body built for performance, but a brain that’s always looking for efficiency.” We live or die by our endurance, but remember: endurance is all about conserving energy, and that’s the brain’s department. “The reason some people use their genetic gift for running and others don’t is because the brain is a bargain shopper.”