Nerves make us bomb job interviews, first dates, and SATs. With a presentation looming at work, fear robs us of sleep for days. It paralyzes seasoned concert musicians and freezes rookie cops in tight situations. And yet not everyone cracks. Soldiers keep their heads in combat; firemen rush into burning buildings; unflappable trauma doctors juggle patient after patient. It's not that these people feel no fear; often, in fact, they're riddled with...