As investors rip another page off of the calendar on Thursday, many will think twice about holding on to their stocks. That's because they will be tempted to heed the age-old market aphorism "sell in May and go away"—which, in its fullest version, instructs investors to abandon equities before May in favor of risk-free Treasury bonds, before switching back into stocks in November.
"For being something you would think that professionals would maybe take with a big grain of salt, it gets a tremendous amount of play," said ConvergEx Group's chief market strategist, Nicholas Colas. "We've talked about it on our morning call for the last five days, because our accounts all talk about it."
But Colas says it's not exactly an investable thesis.
"You can't just close your eyes and use a nursery rhyme to invest," Colas told CNBC.com. "You have to look at why it might be similar or different this year. We respect history, but everything about this market over the past five years has been a series of interesting and one-off anomalies—the most obvious example of which is Fed policy."
As to the history he's referring to, it certainly tells a bearish tale about the period between May Day and Halloween. Over the past 36 years, the S&P 500 has risen by an average of 1.3 percent each month in the November-to-April half of the year, but only 0.3 percent per month in the worse May-to-October half of the year.