The S&P 500 (SNPINDEX: ^GSPC) has soared higher over the past few months, putting the famous stock market index up 18% over the past year. At approximately 20.4 times expected earnings, the S&P 500 has become notably more expensive than its 30-year average of 17.2. In other words, history shows that there's an opportunity cost in withholding your money from the stock market. A recent paper from J.P. Morgan Asset Management found that the S&P 500 has experienced an average intra-year drop of 14.2% from 1980 to mid-2026. So, if you hold a popular index fund, like the Vanguard S&P 500 ETF or State Street SPDR S&P 500 ETF Trust, it's going to fall from its high quite often.