Instead of thinking carefully about things, we take cognitive shortcuts.  We use mental “rules of thumb”, and we do so because, come on maaaan, if you thought carefully about EVERYTHING, life would suck.  Life is way too complicated; there’s too much uncertainty in the world; and who has the time for that anyway?  Just “use common sense” and get on with things.  

Right?

Well, unfortunately, sometimes this could lead you to murdering somebody (unintentionally, in this case).  It’s also a HUGE contributor to addiction (and almost everyone you know, including you probably, is addicted to things).  It even can lead to suicide.  And much of this could be avoided if people just understood, like really understood, the boring-sounding Representativeness Heuristic.