When I first turned 18 my dad took me to a casino and I thought, "Oh, this is great.  We're going to have some father-son bonding time, but he really just wanted me to learn an expensive lesson in economics.  We sat down at the blackjack table, and I'm not very good, so I started losing pretty early on, and he's like, "Here, go ahead, you can borrow some of my chips."  So I took his, and I lost those too, and then at the end of the day he's like, "Hey, are you going to pay me back?"  I was like, "Wait, you wanted money back?"  And I ended up losing quite a bit of money that day, and I haven't gone to a casino since then.  The idea of spending more money than you have, spending someone else's money, is rarely a good idea in economics, but I think that's the main cause of the problems that we're seeing today in the housing industry.