http://money.howstuffworks.com/pyramid-scheme.htm
You're outside cutting the lawn and your neighbor pulls up in a brand-new BMW. He's wearing a suit and carrying a briefcase. You've never seen this guy out of his sweatpants. Maybe a millionaire uncle died?
After some small talk, you ask him what's up with the new car and the new suit. He acts all coy and says he just got lucky with a new type of business opportunity. You're curious, so you ask for more details.
He says he's become a freelance distributor for a health supplement company. Turns out that there are tons of people out there who will pay big bucks for his products. And even better, the more salesmen he hires to work for him, the more money he makes. For a one-time sign-up fee, plus the cost of the merchandise, you could start doing the same thing tomorrow. "Hire 10 salesmen," he says, "And you'll have your own BMW in a month."