Why soldiers so often do nothing in battle

In the Close Combat computer games there is psychology. SS troops fight to the death whilst ad hoc units get mortared, scared and can run away.

That would be an interesting, albeit probably frustrating mechanic to put into a tactical wargame...

Fighting, flighting, freezing and faffing...describes much of my everyday life. Though have to admit, I'm rubbish at fighting; good thing I'm not a soldier.