Let's face it: Investors put money to work in the stock market with a single core goal -- to achieve strong returns and grow those funds. And over the long term, a diversified portfolio can certainly do just that. Over the past two decades, the S&P 500 index has registered a 557% total return. But that is, of course, the average result from a large group of companies. Some have produced drastically better gains.For example, a $10,000 investment made exactly 20 years ago in one business that has since become ...