The final reason behind the forecast revisions is probably America's flexible labour market. The fall in unemployment in recent months seems to reflect more new jobs, rather than discouraged workers exiting the workforce. In Europe governments have tended to assume much of the payroll cost for furloughed workers. Such schemes are handy in a tight spot. But if prolonged, they could keep workers in jobs that are never coming back. America, by contrast, has mainly protected people's incomes with unemployment benefits (although it has absorbed the payroll costs of many small businesses via loans that may eventually be forgiven). As a result the reallocation of labour from dying industries to up-and-coming ones is happening at speed. For example, the number of travel agents has fallen by 10% since April, even as overall employment has risen. Employment in general-merchandise shops is 6% higher than before the pandemic.
Much could still go wrong. The virus could surge again, as it has in Europe. Many forecasters continue to assume, optimistically, that Congress will pass another stimulus package this year. Americans cannot run down their savings forever. And socialdistancing requirements remain in place in much of the country. As a result some labour-market indicators still look dire. In August, even as the overall unemployment rate fell, roughly 3.4m jobs were permanently culled, more than in October 2008, soon after Lehman Brothers collapsed. The rapid rebound this time could yet hit a hard ceiling. But Mr Christensen's optimism no longer looks so exceptional.