Commandment No. 6: No Sale? No Profit

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.

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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 Quote) 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 Quote). 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.