"Situational awareness and perception" training, experience and instinct.
Another reason for a perception secondary characteristic
Good training reduces the impact of stress, so lessening the effects of hypervigilance, so enabling more reasoning during those sorts of situations. Good reactions save friendly lives, but clear thinking beats the side that is only ever reacting.
Eg: TB in the wilds of AFG would put fire onto our advancing section patrols, which would then shake out into line of assault while the TB sent a flanking force around to put enfilade fire onto the assault line when it was preparing to launch into the original TB firers, almost always faster than an assault line could put in the attack. The trick was to send a counter-flanking force out immediately on taking EN fire and effectively ambush the TB as they tried to effect their hook or assault their flanking fire support position. Cool thinking beat fast reactions.
I think this has always been a difficult thing for games to simulate. I thought 2300 AD's character skill Coolness Under Fire was a great idea, but there should be a limit where someone is only just so cool before they become unhinged or unbalanced.
