For the last 15 years, all you've needed to do to achieve double-digit returns on your money was park it in an S&P 500 index fund, reinvest dividends, and forget about it. That happy ride may be over,

The S&P 500's CAPE ratio has averaged 22%, Goldman said. Second, market concentration is near its highest level in 100 years, Goldman said. "When equity market concentration is high, performance of the aggregate index is strongly dictated by the prospects ...

During the next ten years, the S&P 500 (which reflects the broader market) could yield a nominal annualized return of 3%, analysts at the investment bank predicted in a note from Oct. 18. The analysts placed a negative 1% annualized nominal return at the low end of the range of likely outcomes,