Financial Arbitrage, Bernie Madoff and Free Lunches

Although we all would like to earn arbitrage profits, there probably aren't too many real-world opportunities to do so. I guess I am one of those people who believes the efficient market theory is approximately correct. Or the version I like to tell my students - "There may be individuals who can generate riskless excessive returns. But chances are, you're not one of them." Ed Glaeser argues that the searches for these profits leads people into getting suckered by scam artists such as Bernie Madoff:

If the lesson of the current crisis were that there were plenty of opportunities for arbitrage, then ordinary investors might conclude that they can beat the market, either by finding loopholes themselves or by investing with money managers who are skilled enough to beat the market. This type of logic led so many to trust their money with Bernie Madoff and his ilk.

If an investment seems to good to be true, then you have to wonder if it is really just a Ponzi scheme.