Stocks go up and down, but eventually, most go up. So if you invest and hold on, odds are you'll do quite well. As my former Princeton economics professor, Burton Malkiel, told me, "The stock market is like a gambling casino with the odds in your favor. Over the long pull, it beats inflation, and beats it by a great deal."

 If you want to beat other investors, too, it's logical to think that you should turn to the most visible specialists for advice. These men and women make their living studying stocks, and they sound so confident on CNBC. You'd think they could beat the market.

 Don't bet on it.

 "Most of the guys on TV -- they're not that good," said Jim Cramer. He should know: He's all over the place talking about investing -- CNBC, CBS Radio, the Web, bookstore shelves, and New York magazine. Cramer told me that he is different from other stock-pickers because he has no hidden motives.

 "A guy comes on TV," said Cramer. "Thought process at home: 'There's a person who has looked at the whole industry and is making judgments about what are the best stocks.' Wrong! Wrong! The worst are guys who say that they love a stock and they're selling the stock. That happens all the time."

 Then there are the guys who pump the stocks of companies with whom they're doing business.

 CNBC's "Guidelines for Appearances by Financial Professionals" now require its experts to tell it, so it can tell you, about any ties they have to the companies they discuss. But even the scrupulous expert, the one who's not touting his friends or customers, is unlikely to give you much of an edge.

 "I ended up losing just over $40,000," trailer park manager David Talevi told "20/20." That was a year's salary for him. He lost it buying stocks they recommended on TV. "You just took their word for granted," he said. "I figured, you know, 'This thing is going to take off.'"

 "This thing" crashed instead.

 How could the TV experts be so wrong? They are well-educated people who call and visit individual companies, and study the balance sheets, new products, and marketing techniques. They work at this full time. You'd think this would give them an advantage. But it doesn't, Professor Malkiel said, because what they learn is information all the analysts have. Malkiel wrote a book about the process called "A Random Walk Down Wall Street." He studied stock movements of the past, and concluded that the advice produced by the in-house experts has little value. "Most of it is just absolute nonsense," he told me, "and most of it is really designed to get people to trade more than they should." Continued...