"If you put your money in the stock market over the past decade, for example, your return would be zero."
Another reason to look into a more balanced approach than just stocks. If you, for instance, put 70% in stocks and 30% in long term US treasure bonds and rebalanced at the end of ever year (simplicity of calculations), you would be looking at about 1.5x the amount at the end of 2010 from the start of 2000. Such an approach is likely to worsen your overall returns a bit (see: the 90s), but it also noticeably reduces the volatility.
Another reason to look into a more balanced approach than just stocks. If you, for instance, put 70% in stocks and 30% in long term US treasure bonds and rebalanced at the end of ever year (simplicity of calculations), you would be looking at about 1.5x the amount at the end of 2010 from the start of 2000. Such an approach is likely to worsen your overall returns a bit (see: the 90s), but it also noticeably reduces the volatility.