A staggering 20 million Americans lost their jobs in April and yet the US stock market had its best month for decades, with the S&P 500 up 13 percent. Since then job losses have continued to mount, and yet the market is still higher. How can US shares be doing so well when the evidence of economic devastation is overwhelming?

Even odder, the US stock market (S&P 500, down 13 percent year to date) is doing far better than the UK (FTSE 100, down 23 percent YTD) and European indices (Eurostoxx, down 26 percent YTD), and yet UK and European governments...