Dan - in all walks of life fear is a great motivator. Fear takes many shapes and motivates in different ways. It is fear of being killed, captured, or being called a coward that motivates some uniformed persons to do great things in their own mind. Fear motives defense, cowardice, courage, and .. the big one - inaction. Most military personnel are trained to conquer or control their fear and use it as motivation to do heroic things. The big difference in dogs is the need for self preservation which lead some to run away because they know they cannot survive the conflict or motivates the defense in the ones that think they can or have no escape. I think you know it is much more complicated than that from a genetic or physiological standpoint - so I'll wait for more comments. Fear is a great motivator for all things in life - me thinks.