Take a look at how much the performance of U.S. stocks has varied over the past five years: only 19 S&P 500 components have declined more than 50%, while on the other end, 135 stocks have doubled in value. The market has become so polarized that the performance of different sectors is essentially two different worlds. For those focused on global asset allocation, this data really highlights the issue — not all stocks can keep pace with the overall market.