From the graph it looks to me like the entirety of the gain comes from skipping some of the 2008 financial crisis. http://www.agoraopus.com/wp-content/uploads/

From the graph it looks to me like the entirety of the gain comes from skipping some of the 2008 financial crisis. http://www.agoraopus.com/wp-content/uploads/2015/04/Sell_in_May_vs_Buy_and_Hold.png http://www.agoraopus.com/wp-content/uploads/2015/04/Sell_in_...