Editor's note: This is a special sneak preview of Jim Cramer's just-released book,

Jim Cramer's Stay Mad for Life: Get Rich, Stay Rich (Make Your Kids Even Richer)

. Look for more sneak previews every day, and get your free copy with your annual subscription to Action Alerts PLUS; click here for details. Catch Cramer in person at his last book signing event: Saturday, Jan. 12, at 1 p.m. in Westbury, Long Island's Costco. Missed the first sneak previews? Read the book intro and the rules of getting and staying rich: Rule 1, Rule 2, Rule 3, Rule 4 and Rule 5. Know what pros do right and amateurs do wrong: Part 1, Part 2, Part 3, Part 4 and Part 5. Learn the five mini-bull markets that will stampede for years, starting with aerospace and defense, agriculture, oil and oil service, minerals and mining and infrastructure.

3. Pros try not to invest in things they don't know.

TST Recommends

They are not anxious to risk their hard-earned capital on something that sounds cool. Taking passes is the best thing I do. So many people ask me about different stocks, but many stocks are beyond my ken. I just recognize they are not my strength. I am a generalist who takes pride in knowing more stocks than anyone in the universe.

Hardly a day goes by when someone doesn't ask me about some stock that has a miniaturization method, a nanotech derivative. I know better. I recommended one,

Tessera Technologies

(TSRA)

, and the week after my recommendation it lost 20 percent of its value on something that, frankly, I simply did not understand, some piece of technology that was just too hard to know unless you were using it as a client.

Same thing goes for a lot of the wide-area network stocks -- stocks that help remote workers tie in with headquarters. These are jargon-filled black holes that you need an information technology expert to walk you through.

Cramer: Pay for Your Kids' College -- All of It

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Lots of the biotech stocks leave me cold; I don't understand how the medicines they make are special or different and how the companies themselves can be sure that they work.

I also never think I can get an edge in commodities, even though so many people want me to tell them what I think of the direction of wheat or corn or soybeans -- yes, I actually get asked that.

I just accept the fact that I don't know it, that it is too hard for me to learn, and I take a pass. Too many people feel embarrassed to take a pass. Not me. I am always willing to say, "Nope, I don't get it, I don't understand it, and I don't want to trade it."

Don't think that everything has to be traded or owned. Some things are genuinely too hard for you to know. In

Magnum Force

, Clint Eastwood summed it up well: "A man's got to know his own limitations." I know mine.

Do you know yours?

Editor's note: This is a special sneak preview of Jim Cramer's just-released book,

Jim Cramer's Stay Mad for Life: Get Rich, Stay Rich (Make Your Kids Even Richer)

. Look for more sneak previews every day, and get your free copy with your annual subscription to Action Alerts PLUS; click here for details. Catch Cramer in person to get it signed: Wednesday, Dec. 12, at 7 p.m. in Bridgewater, N.J.'s Borders; and Saturday, Jan. 12, at 1 p.m. in Westbury, Long Island's Costco. Missed the first sneak previews? Read the book intro and the rules of getting and staying rich: Rule 1, Rule 2, Rule 3, Rule 4 and Rule 5. Know what pros do right and amateurs do wrong: Part 1 and Part 2.

From Jim Cramer's Stay Mad for Life by James J. Cramer and Cliff Mason. Copyright

2007 by Jim Cramer. Reprinted by permission of Simon & Schuster, Inc.

At the time of publication, Cramer had no positions in any of the stocks mentioned in this column.

Jim Cramer is a director and co-founder of TheStreet.com. He contributes daily market commentary for TheStreet.com's sites and serves as an adviser to the company's CEO. Outside contributing columnists for TheStreet.com and RealMoney.com, including Cramer, may, from time to time, write about stocks in which they have a position. In such cases, appropriate disclosure is made. To see his personal portfolio and find out what trades Cramer will make before he makes them, sign up for

Action Alerts PLUS. Watch Cramer on "Mad Money" weeknights on CNBC. To order Cramer's newest book -- "Jim Cramer's Stay Mad for Life: Get Rich, Stay Rich (Make Your Kids Even Richer),"

click here. Click

here to order "Mad Money: Watch TV, Get Rich," click

here to order "Real Money: Sane Investing in an Insane World," click

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here for Cramer's autobiography, "Confessions of a Street Addict." While he cannot provide personalized investment advice or recommendations, he appreciates your feedback and invites you to send comments by

clicking here.

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