Smith [the company commander] did not have to order his Marines straight into the direction of the fire; it was a collective impulse - a phenomenon I would see again and again over the coming days. The idea that Marines are trained to break down doors, to seize beachheads and other territory, was an abstraction until I was there to experience it. Running into fire rather than seeking cover from it goes counter to every human survival instinct - trust me ... In one flash, as we charged across [the street] amid whistling incoming shots, I realized that they were not like me; they were Marines.

In the Line of Fire
Robert D. Kaplan