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 "Ten Commandments of Trading." For more about the new book and to order it, click here. To learn his "Twenty-Five Rules of Investing," click here. To read Cramer's first commandment, click here. To read Cramer's second commandment, click here. To read Cramer's third commandment, click here. To read Cramer's fourth commandment, click here. To read Cramer's fifth commandment, click here. Today, we present Cramer's sixth commandment.

The game's tough right now. So tough that you have to be thinking, "It's just not worth it. When 50,000 people close accounts at

Ameritrade

(AMTD) - Get Report

in a quarter, you have to know that you aren't suffering your misery all by your lonesome.

It's always that way when you are

rooting for bad news. It's always that way when you are

playing defense.

This is one of those moments when people are looking at some rather huge gains in sectors that may be giving way and they don't want to ring the register.

All of you in that situation, I want you to remember one of my most important Trading Commandments:

You don't have a profit until you sell.

The way this market looks right now, if you have a big gain in one of these heavy cyclical stocks, you need to think about whether that gain is going to get wiped out or not.

Let's take

Phelps Dodge

(PD) - Get Report

. I genuinely feel that those who bought Phelps Dodge in the $60s and $70s believe that they are so far away from where they bought the stock that they

have

the gain. You do not have the gain until you take it. And some needs to be taken.

If we truly are in rotational hell -- which I think we are, by the way -- you have got to take some of the cyclical winnings off the table, you just have to. Right now, right here.

Stop thinking that you have it in the bank. Instead,

put

it in the bank. And accept the fact that the offense has made about all it can here and you have to be defensive to play the next move correctly.

James J. 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 by

clicking here. While he cannot provide personalized investment advice or recommendations, he invites you to send comments on his column to

jjcletters@thestreet.com. Listen to Cramer's RealMoney Radio show on your computer; just click

here. Watch Cramer on "Mad Money" at 6 p.m. ET weeknights on CNBC. Click

here to order Cramer's latest book, "Real Money: Sane Investing in an Insane World," click

here to get his second book, "You Got Screwed!" and click

here to order Cramer's autobiography, "Confessions of a Street Addict."