It is very stable only over the VERY long haul. Look at the SPY index, which is total returns (including dividends) of the S&P. Take it back to 1994, which is

It is very stable only over the VERY long haul. Look at the SPY index, which is total returns (including dividends) of the S&P. Take it back to 1994, which is as far as Yahoo Finance allows. http://finance.yahoo.com/echarts?s=SPY+Interactive#symbol=spy;range=my;compare=;indicator=volume;charttype=area;crosshair=on;ohlcvalues=0;logscale=off;source=undefined; http://finance.yahoo.com/echarts?s=SPY+Interactive#symbol=sp... In the almost 20 years since, there are many 5 year periods of rapid drops, and many flat 10 year periods. If you look as the NASDAQ it gets much worse. One can say, "It's been a rare 20 years" but who are we to say the business environment pre-1994 is more similar today than post-1994? I think you can't speculate on what the future will look like, you have to prepare yourself for the uncertainty. (Invest in yourself and your health, prepare for the possibility of retiring later, don't ignore your spouse so much that they divorce you, etc.)