"Sell in May and go away," is one of the very best, of a very few, meaningful Wall Street sayings. The lesser-known completion is, "Do remember to buy in November." Thus, the year is broken into two parts: May - October, when you should be out of the stock market, and November - April, when you should be invested in stocks.
The first chart below shows the performance of the each of the two periods over the last 35 years. "Random" is the word that first comes to mind, but with a little study, the savage '70s can be seen, as can be the truly remarkable, nifty '90s. But, to see the real value of this axiom, look at the second chart.
"Wow!," is the word that comes to mind.
Unfortunately, May is now upon us, and history suggests a difficult six months.
It goes without saying, but we'll say it anyway: anything can happen in any given year. But, as someone [Damon Runyon?] once put it, "The race does not always go to the swift, nor the battle to the strong, but that's the way to bet."
Go away, and have a nice summer.