Japan knows about bad days in the stock market. From its peak in 1990 to last June, Japanese equities lost three-quarters of their value. Even so, yesterday’s 7.3 per cent plunge in the Nikkei 225 Average stood out as the 11th-biggest drop since the measure was created in 1950.

Explanations abound for the fall. Loose talk of the Federal Reserve retreating from bond purchases in America helped drive up US bond yields, which could have helped Japanese 10-year yields hit 1 per cent for the first time since April last year. Surprisingly weak economic data from China sparked another plunge in commodity prices. Haruhiko Kuroda, Bank of Japan governor, disappointed some by failing to suggest new moves to combat rising bond yields.

None of these explanations really cuts it. Bond yields have been rising along with equities and yesterday tracked share prices perfectly as they moved down again.