Fear of a Female Planet

In the book On Killing (and excellent book, BTW, about how the military learned to override the aversion that most humans have to killing other people, and the long-term social costs), the author has a really interesting section on combat vigilance. Back around WWII, it was discovered that a soldier's chances of survival got steadily better for the first month of being in an active combat situation. Part of it was the fact that, to be crude, the dumb ones got weeded out early. But part of it was that they learned that intuitive sense of the battlefield, and could instinctively avoid danger. After about a month, though, they would plateau and not get any better, as the same stresses that helped them adapt started overwhelming them. After hitting that one month mark, if soldiers are not rotated out for some relief, they still have that intuitive vigilance, but in some small way, they stop caring whether they live or die, and start making stupid mistakes.