Take someone who was doing pretty good during the tech and real estate bubbles, and decided to invest their spare change in 1998, 1999, 2005 and 2006, but did not invest in the "leaner" years. I bet that person overall would have lost money on the stock market. Oh, wait, I can tell you that that person would have lost money, because it was me!
I'm so tired of the constant drum-beat of "The only way to retire is to invest in the stock market!!" that only seems to serve the interests of Wall Street. I wish there were viable alternatives.