But there's a problem," Dr. Bramble said. He tapped his forehad. "And it's right up here." 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.