Seasonal variations in investors’ moods impact stock market returns, according to new studies. : Economist John Maynard Keynes said that “animal spirits” move the markets, but maybe the sun and the clouds have something to do with it, too. In his “General Theory of Employment, Interest and Money” Keynes wrote, “The markets are moved by animal spirits and, not by reason.” This quote, which is widely printed in economics textbooks, serves to warn students that investors are not always rational went it comes to their investment decisions.