Last January, no one predicted a global pandemic was about to clobber the world economy but that stock markets would gain anyway. Nevertheless, here we are.

Last week, the S&P 500, down 31 per cent for the year at its March lows, climbed into positive territory for 2020. There has never been a year where stocks gained after being down at least 30 per cent at some point, according to LPL Research's Ryan Detrick, so this is some turnaround.

Now, you could say the figures are distorted by the huge gains recorded by a handful of mega-cap stocks like Apple and Amazon. Most US stocks have actually declined in 2020; according to JonesTrading strategist Michael O'Rourke, for every S&P 500 stock that has advanced this year, 1.7 have declined. However, US indices are not the only 2020 gainers. China's Shanghai Composite Index has gained 10 per cent. Denmark's OMX Copenhagen 20 is up 17 per cent. Sweden's OMX Stockholm 30 has crept into positive territory. So too has Germany's Dax, following a mammoth 60 per cent run off its March lows. Is there a lesson in this? Yes, and it's not that investors are mad, or that central banks have taken over financial markets, or whatever argument takes your fancy.

The real lesson is simple yet profound: we didn't anticipate this because the world is, as Nobel laureate Daniel Kahneman once pointed out, difficult to anticipate. To quote Kahneman, "That's the correct lesson to learn from surprises – that the world is surprising."