Rule No. 11: Don't Own Too Many Names

Editor's note: Jim Cramer's new book, Real Money: Sane Investing in an Insane World, is available in selected bookstores now. As a special bonus to RealMoney readers, we will be running Cramer's "Twenty-Five Rules of Investing." For more about the new book and to order it, click here. Today, we present Cramer's eleventh rule of investing. Read more about his rules:

1. Pigs Get Slaughtered
2. It's OK to Pay the Taxes
3. Don't Buy All at Once
4. Buy Damaged Stocks
5. Diversify to Control Risk
6. Do Your Homework
7. Don't Panic
8. Buy Best-of-Breed
9. Defend Some Stocks
10. Don't Bet on Bad Stocks

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In my years as a hedge fund manager, I spent three hours every day analyzing the mistakes of the day before. That was my major task, one that I completed before anyone else came into the office, generally between 4 a.m. and 7 a.m. I would analyze every losing trade -- you don't need to analyze the winners, they take care of themselves -- and try to figure out how I could have made more money or lost less money. ...