Looking at the line chart as a whole, the S&P 500 has gone through long periods of good returns (green boxes) alternating with just as long periods of bad returns (red boxes). For the 111+ years, the time spent in good periods is nearly the same length as time spent in bad periods; 55+ years. It isn’t hard to imagine that at 8.5 years minimum historically, the good and bad periods lasted long enough to condition investors to expect the same indefinitely.
https://www.advisorperspectives.com/articles/2021/04/26/the-stock-markets-collapse-is-near
