Herbalife, a company that sells weight loss shakes, vitamins and other similar products, is worth billions of dollars. The company has been around for more than 30 years, and it’s traded on the New York Stock Exchange. Bill Ackman thinks the whole thing is a pyramid scheme.Not surprisingly, Herbalife disagrees. Ackman manages a hedge fund that has shorted more than a billion dollars’ worth of Herbalife stock. If the stock falls — and Ackman says he thinks it will fall all the way to zero — the fund will make money. On today’s show, we talk to Ackman and to Herbalife. And we consider what it means when an investor bets that a company will fail.