RealMoney Radio Recap: Piece by Piece

"Buy weakness. Sell strength," Jim Cramer told his "RealMoney" radio show listeners Tuesday.

It's a mantra he repeats often, and he said it again because many people who bought stocks when prices were going up got crushed in the latest market selloff.

Commodities and their related stocks were up a tremendous amount since the beginning of the year, he said. These commodities include zinc, steel, copper, gold, silver and aluminum, along with industries like mining and companies that make earth-moving and safety products.

He said that this is all part of the commodities complex and that the complex has been soaring because developing nations of the world need these building blocks to develop their infrastructures.

Investors who bought this complex low and started scaling out last week did not get crushed by this selloff, he said. They sold into strength. "Scaling out" means selling out of a position in pieces.

But a lot of people bought into the commodities complex after it had already moved considerably higher, hoping that it would just continue to climb.

So, when these stocks took a swan dive, traders who bought them up had no choice but to panic, he said. For example, if an investor paid $102 for Phelps Dodge(PD Quote) five days ago and then watched it go to $87 just a few days later, of course, panic set in.

Cramer said that the trick is not only to scale out of stocks as they grow very strong, but to also pick up stocks when people are panicking and taking the prices down.

Soon, we'll be able to start buying these stocks again in steps, he said, adding that investors who sold some of these stocks in a panic can start picking them up again now that the price is lower.