Sell in May and go away

Traders, like everyone else takes holidays, and it appears they do so in the summer. As such, there is an existing theory that bullish traders take a break during the summer and early autumn months and that stocks will typically fall until just before the winter holidays.

With that said, in 2021, the S&P rose 10% between the start of May and the end of October, and has averaged a 5.7% gain between May and October over the past decade. The only time the market fell in that period was in 2015.

This, however, speaks to potential timing effects on stock price. They clearly exists within a day, and week, and according to this idea, year.