The urge to purchase non-essential items stems from an urge to better one's self, mainly by altering or reinventing one's persona. The cycle goes like this:
Seeing an item -> Picturing one's self with the item -> applying the associations of the item to the context of your own life -> evaluating whether these associations could be attainable -> purchasing the item with the view of changing one's character -> trying out these new associations for the first time and, to a degree, believing it has worked -> after a while, the new item becomes commonplace -> human nature and a strongly conditioned, pre-existing personality comes back, overriding the influence of the new item -> the search for a newer item begins, the customer starts looking for an item with associations strong enough to override human nature and break the cycle -> the cycle begins again, identical every time.
The most important part of this cycle is the associations drawn between items and people. The media is the all encompassing associative tool and these associations are far more important than the functionality or quality of the item in itself.