The covenant of mortgage

...,we all believe that we have an ethical and moral obligation to pay the bill each month. If people stop believing that, then the entire system is at risk. Imagine if 20 million or 30 million people whose homes are worth less than their mortgages simply walked away and handed the keys back to the banks and mortgage brokers.

And yet that is precisely what the smart guys on Wall Street do because for them, if an investment doesn't make financial sense, it makes more sense to walk away than to keep pouring good money after bad.