The study looks at "lifetime returns to every U.S. common stock traded on the New York and American stock exchanges and the Nasdaq since 1926." To reconcile the thread title with the fact that the stock market has been a good investment historically, remember that the lognormal distribution has high positive skew for large values of the standard deviation parameter, so that the mean is much higher than the median. Also note that you don't need to reinvest the dividends of a stock in the same stock -- you can invest in the broad market through an index fund.