From Investorplace:
Generally speaking, May isn’t a great month for stocks, but that shouldn’t preclude you from looking for high-quality stocks to buy that typically buck the bearish trend.
There’s a reason the phrase “Sell in May and go away” has become a key consideration for traders. On average, the S&P 500 loses 0.2% for the month that just recently got underway, making it one of only two net-losing months of the year — September is the other.
Even so, that modest lull is misleading.