Heres a quote from Splinter Cell:
Myth: The deciding factor in a contact is firepower
Reality: Trading firepower for mobility increases life expectancy in combat.
Remember, surprise is decisive and you must be decisive; travel light, conserve ammunition, and above all keep moving, because you won't know if you're in a bad position until you've stopped in one. And one more thing: when under fire, reposition, then reacquire.