Sneak Preview: Admit It When It's Too Hard

Editor's note: This is a special excerpt from Jim Cramer's book, Jim Cramer's Mad Money: Watch TV, Get Rich. To order your copy and read all the rules, click here.

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5. Don't be afraid to say it's too hard: some things like restaurant same-store sales, are just too difficult to game. There are hundreds of different ways to make money in the market, but not everything is worth betting on. There are some metrics that are just too hard to predict, and that means you shouldn't try to invest based on them.

The hedge funds will try to game anything and everything, but that doesn't mean they have a method that works; it just means that they're willing to place big bets all over the place to try to make big money. But that makes everything in the market much more volatile than it used to be.

From my experience on the show, the hardest metric to game, the one I think you should avoid trying to predict altogether, is same-store sales in the food-service business. There are hundreds of hedge funds that will try to figure out which way the same-store sales of restaurant stocks will go, and those funds will either buy large positions in the restaurant stocks or sell a lot of shares short depending on whether they're positive or negative about the numbers.

This creates volatility. All the hedge fund guys who get it wrong will close out their positions, either by selling if the stock is down or by buying stock to cover their shorts if the stock is up. That makes betting on restaurant sales a dangerous game: you could make a lot of money or the stock could blow up in your face.