Diversify. That was the mantra investors heard in recent years. Investing in a range of assets was supposed to improve overall returns because these were uncorrelated bets. Baloney. This year world stock markets lost almost $30,000bn in value. Oil prices fell by two-thirds. House prices dropped. Bonds – except government bonds – collapsed. And poor November sales at Christies and Sotheby’s showed the art market turning too. Almost every asset performed alike in 2008: it went down.

This was unusual. Normally assets have their moment in the investment sun depending on the stage of the economic cycle. Bonds and defensive stocks, such as utilities, perform well going into a recession. Growth stocks do best coming out. So-called emotional assets, such as paintings, supposedly have no link to the economic cycle at all. This year everything happened simultaneously. Correlations converged on one.