Editor's Note: This is a recap of a program that was orginally broadcast on Good Friday, April 14.
Shares of Crystallex ( KRY), which operates the biggest gold mine on Earth, have more than doubled since the year began, Jim Cramer said on his "RealMoney" radio show Friday. But Cramer said he wants use Crystallex to teach people a very important lesson regarding the time frame of stocks. Market players should buy weakness and sell strength, he said. Although people always talk about buying low and selling high, they like to buy high and hope the stock goes higher. But they need to think about the time frame. When you do your homework and think of going into a company, take advantage of market fluctuations, he said. "When stocks are sliding, you should be interested in buying, and when they are soaring, you should be interested in selling," Cramer said. "It's about facts and doing it right, increasing the odds and making money." An approach that might make you money is looking six to 18 months ahead of when you buy a stock, he said. By nature, Cramer said, he is impatient and wants to make money now. He said he's been talking about Crystallex for weeks, and has even talked with the company's CEO. If people decided to get into the company, they might have bought it around $6, and then it went down to $5. Now, some people might be worried about the price slide, he said, adding he knows this because many people wrote to him asking what was going on with the company one day after it started dropping. I know no one likes to lose money, but during price fluctuations nothing has changed with the company. Since April 14, the stock has fallen to $2.87 . Cramer said he believes people should buy Crystallex while it's coming down because essentially it is a huge gold mine with gold 18 inches below the surface.