What we in the western world are about to learn is that there is no such thing as a Keynesian free lunch. Deficits did not “save” us half so much as monetary policy—zero interest rates plus quantitative easing—did. First, the impact of government spending (the hallowed “multiplier”) has been much less than the proponents of stimulus hoped. Second, there is a good deal of “leakage” from open economies in a globalised world. Last, crucially, explosions of public debt incur bills that fall due much sooner than we expect.