The subprime market contained the hallmark of every Ponzi scheme. It worked only as long as more money was put into the scheme. When home prices were rising, overextended borrowers usually could pay off their first mortgage-and often a home-equity loan and credit-card bills on top of that-by selling their house in a rising market. Once home prices stopped rising, the game was over, and home prices would plummet.From: Confidence Game: How a Hedge Fund Manager Called Wall Street's Bluff. If you're a fan of William Ackman, you must read this book!