Individuals disposed toward risk-taking are probably better suited for particularly dangerous deployments and missions. But those same individuals are poorly suited for other aspects of military life, or less exciting military vocations, according to a landmark 2000 study by U.S. Army Maj. Michael Russell. He proposed that there were two primary military personalities: soldiers who exhibited a need for action and unpredictability (high stimulus-seeking) and people who were attracted to the military because its life offers a high degree of structure and discipline. A military needs both types to perform at peak but therein lies a fundamental contradiction. Military life is incredibly structured. War is unstructured. The stronger your attraction to one set of stimuli on the spectrum, the greater your aversion to the other.