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NEW YORK ( TheStreet) -- "When you own stocks, you need to be humble," Jim Cramer told "Mad Money" TV show viewers Monday, as he dedicated the entire show to helping investors protect their profits from things they likely never saw coming. Cramer said that at some point something is going to go wrong with every portfolio, which is why diversification remains the single most important concept in investing. The traditional view of diversification means that no more than 20% of your portfolio can be in any given sector. So if you own five stocks, that means only one tech stock, one health-care name, on financial, etc. Investors need to err on the side of caution, said Cramer. Oil producers and oil refiners may be different, but their success and failure both ride on the price of oil, which make them the same. Hardware and software are both technology, which make them the same as well. But beyond the traditional views on diversification, Cramer said investors need to take it a step further and make sure their portfolios can win in any market, and that means owning some gold along with a high-yielding dividend stock, a growth stock, a speculative stock and a foreign stock. Cover all these bases and a portfolio will be bullet-proof, Cramer said. Why gold? Cramer said that gold is a special case because it tends to go up when everything else goes down. Think of it as stock insurance, he said, a safe haven. He continued to recommend the SPDR Gold Shares ( GLD), as owning the gold miners themselves has proven to be too risky.