The world is a dangerous place and recent events have served to make it less safe. There are many arenas of conflict and even combat across the world. Such situations are the quintessential expression of stress; you stand in imminent danger and live with the knowledge that you may be attacked, injured or even killed at any moment. How do people perform under these conditions? How do they keep a heightened level of vigilance when nothing may happen in their immediate location for weeks or even months? What happens when the bullets actually start flying? How is it you distinguish friend from...