The reason is simple a lot of your work, time and energy drains into paying the most scary thing invented by finance industry so far - 'Compound Interest'. This is especially dangerous in the case of credit card. The debt keeps mounting because of two reason, you being unable to pay and yet still continuing to borrow money. This sort of a spending patters brings a lot of pain to people every where.
And all of this for what? Upgrading from iPhone 4 to iPhone 4s. Is this really worth?
In this sort of set up people living with a savings driven life get a automatic lead ahead of spendings driven people.
Because while you are working to pay off the interest money. He works for the same time and saves that interest money.
I think it will be safe to say to say that if your paying X% money as interest to bank by working for hours Y(Remember you are loosing X% money, thereby in effect rendering your Y hours of work useless, as though it never happenned). The same X% is the money earned by the savings driven guy in the same Y hours(Additional to the money he is already earning. So this his extra income).
You work to loose money and he works to get rich. Although both work for the same time. One gets richer other gets poorer. This is how bad debt can inflict suffering on you.
These days you can be relatively rich by just saving money! And avoiding debt.
Borrowing for consumption is where people make the mistake.
So, the question is, which is cheaper? Your mortgage, or your landlord?