Cramer told investors to pay close attention to the direction of the earnings estimates anytime they're investing in growth names. When earnings have momentum, companies can see their stock double in just a year, but if the earnings begin to slow, they will fall sharply, as Chipotle Mexican Grill ( CMG) saw in July when shares tumbled 100 points on the mere suggestion the company may be vulnerable to a weakening U.S. economy.

Speculative Thinking

Every portfolio also needs something to keep you interested, said Cramer, and that means at least one speculative stock. While speculation has become a dirty word on Wall Street, something most financial advisers will tell you to avoid, Cramer said it's important to stay engaged with your stocks and to continue to do your homework, otherwise investing will become no more profitable than gambling.

To speculate wisely, Cramer said investors need to use the right rules and maintain their discipline. Speculation can provide investors with enormous gains, he said, but if done incorrectly can yield gut-wrenching losses.

When it comes to speculating, most investors look towards stocks under $10 a share. Cramer said there are two kinds of stocks in this category: those with broken companies and those with merely broken stocks that have been left for dead by money mangers that aren't allowed to invest in things under $5 a shares. Investors can take great advantage of the latter, said Cramer.

Two great examples of "left for dead" stocks include Ford Motor ( F) and Sallie Mae ( SLM) back in 2009. During the height of the great recession, both companies were hated by Wall Street, sending shares into the single digits.

But beneath all of the skepticism they were solid companies, said Cramer, which is why Sallie Mae was his speculative stock of the year in 2009, when the company's $6 a share stock rose to over $16.

In today's market, Cramer said he's a fan of Sprint Nextel ( S), a stock that had fallen to just $2 a share on bankruptcy rumors, but since then has more than doubled and isn't done going higher.

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