The stock market is the only one in the world where customers gladly plunk down their cash when prices are lofty but run away when there is a big sale. Now the companies that populate US stock exchanges can themselves be accused of such seemingly irrational behaviour.

A year ago, with indices near an all-time high, companies in the S&P 500 were buying their own shares at a record $172bn quarterly pace but are on par to cut this by half or more. This compounds the earnings slump by removing some of the illusory boost to earnings from a reduced share count. More critically, with individuals having turned net sellers of shares since well before last year’s high, companies’ caution on repurchases removes another key prop for prices.