If you believe in inherited wisdom, this is the time of year to dump your stock holdings and take a long vacation: Sell in May, and go away.
Of course, inherited wisdom also held, at varying points in history, that the the earth was flat, the sun revolved around it and draining blood with leeches was an effective way to combat illness.
The reality is usually, at the very least, more complex and nuanced; sometimes, it's altogether different. Read more here.