In a market crisis, opportunity knocks

Big stock market downturns blow off the froth, teach us all lessons, and throw up opportunities

The causes of stock market downturns have been many and varied. But the explosion in derivative markets can magnify them. Last week’s downturn was driven and multiplied by players in those markets whose handiwork can magnify the turbulence, despite no major changes in the fundamentals.

Despite the relatively benign macroeconomic conditions, private investors face much greater danger now than they did before more intrusive and expanded financial regulation. That’s not because of the ...