So, you don’t want to buy just one individual stock because if that individual stock happens to go down—and it can happen—there goes all your money. Diversification is the key.” CNN Money argues, “the core of your stock portfolio should consist of financially strong companies with above-average earnings growth. There are only about 200 stocks that fit that description. A well-balanced stock portfolio should consist of 15 to 20 stocks, across seven or more different industries.”