There have been 20,798 trading sessions between 1928 and today. During that time, the Dow went from 240 to 12,500, or an average annual growth rate of 5% (this doesn't include dividends). If you missed just 20 of the best days during that period, annual returns fall to 2.6%. In other words, half of the compounded gains took place during 0.09% of days.
