Demonstrating a classic mixup between "cover" and "concealment" these Palestinian militia pick a fight and then hide behind this tiny bullet riddled box propped up by small rocks.

An Israeli mail clerk later over-ran this position with a sling shot and a crossman pellet gun. 

As a guideline...if you can see the enemy through the bullet holes they've punched in the object you are hiding behind...then you need to select a different piece of cover.