https://www.forbes.com/sites/investor/2012/04/27/stay-in-stocks-or-sell-in-may/#741083e52185
'Historical performance shows there are best and worst six-month periods for stocks. Jeff Hirsch at the Stock Trader's Almanac calculates that the Dow Jones industrial average has an average return of just 0.3% during the worst six-month period (May through October) since 1950.'