[Whismerhill]

As Kristoffer pointed out,
historicaly
it was difficult to send orders to the troops (much more difficult than now)
and there was often a lack of discipline
you could not say to one soldier : "attack this ennemy rather than the one you're after because it's better for the entire outcome of the battle"

& the soldier will not really have a global overview of the battle so it will chase ennemies, cause of : "blood rush", one ennemy less is still one ennemy less you will not face anymore in the next battle ...
these are typical things in the mind of a rather simple man enrolled in an army to participate into battles they not always understand

feel free to correct me if I'm wrong but that's what illwinter wanted, in my opinion.