When a manager sells a chunk of stock in his own company, other investors often follow: if this guy doesn't believe in the shares, why should we? So Alibaba.com, operator of the world's biggest online bazaar for businesses, saw its shares retreat almost 7 per cent in Hong Kong yesterday after Jack Ma, chairman and chief executive, revealed he had sold about 5 per cent of his holdings.

Were investors right to take fright, wiping about a billion dollars off what was a $14bn company? Insider transactions often foreshadow stock movements: some hedge funds employ analysts tracking little else. Then again, executives are only human. They have calls on their capital, some unexpected; stock sales are not always code for trouble ahead. Mr Ma published a lengthy justification for his first share sale since founding the group a decade ago on the parent company intranet. He expressed a desire to start experiencing “the real meaning and responsibilities of having wealth”.

A reasonable objective, though the timing looks felicitous. Alibaba's recent peak of HK$21.90 a share was almost six times its lows last October. Its forward price/earnings ratio of 65 is almost four times the benchmark, and five times Ebay's. A trailing price/sales multiple of over 29 times puts it in the 99th percentile of Hang Seng stocks. Colleagues of Mr Ma have been offloading shares of the listed company for a while.