If you look at the history of the stock market, you will finds hundreds of patterns which look easy to take advantage of. Some seem to make sense, some make no sense at all. Either way there is a good deal of randomness in how it will turn out next time you see the pattern.
As an illustration of how silly things can get look at this:
Over the last 15 years, stocks beginning with the letter “A” have tended to out-perform stocks beginning with the letter “G”. The difference is more than 100%.
Thus, Alphabet, Apple, Activision Blizzard, Adobe, Amazon, Abbvie, Align Technology, and ASML have been great performers.
The “G” companies like Gazprom, General Dynamics, General Electric, General Mills, General Motors, Gilead Sciences, GlaxoSmithKline, Goldman Sachs, and Glencore have been rather dull.
Is there a reason for this pattern to repeat itself? If you think so, you could just buy the “A” companies, and beat the market without even trying.
The assertion that you should sell in May and go away, is just as silly as the assertion that the "A"s out-perform the "G"s. Note that “Alphabet” used to be called “Google”.
If you want to look for reasons why past patterns worked, you will certainly find them. However there is only a 33% chance that the pattern will repeat next time. There is a 33% chance it will do the exact opposite, and a 33% chance it will do nothing at all.
The remaining 1% chance is that we will all be blown to smithereens and nothing will matter any more.
The more sensible approach is to forget about what the patterns say, forget about interest rates, inflation, wars, labour statistics and other economic data.
Just look at each company and work out “Is it likely to do well in the future?” and “Am I paying a good price for the future stream of growth, dividends and EPS?” If you can answer yes to both, you don’t need to care what the stock market does.