Sell on Rosh Hashanah, buy on Yom Kippur. On average, from 1971 to 2005, the S&P 500 has fallen 0.4 percent between those days, including declines of 2.2 percent in 2005 and 1.9 percent in 2004 (we'll forget about 2006, when the market rose 1.6 percent). As explained by David Gaffen at MarketBeat, the idea is that more investors are closing out positions in advance of the holidays. “Perhaps it’s Talmudic wisdom, but selling stocks before the eight-day span of the high holidays has avoided many declines, especially during uncertain times,” writes Jeffrey Hirsch at the Stock Trader’s Almanac. Old-timers might remember that is used to work in reverse - until it stopped working.