'Don't shoot yourself in the foot with a gun - how hard can that be to understand'? And yet people do it all the time. The 'rule' is easy enough to understand

'Don't shoot yourself in the foot with a gun - how hard can that be to understand'? And yet people do it all the time. The 'rule' is easy enough to understand. But it's not always clear 'why' that is (in many cases, it won't matter), or when exactly it applies. In the lowest common denominator cases, the rule is not so hard to follow, but it can get messy quickly and there are many ways to break the rule.