The many variants of the hangover theory all go something like this: In the beginning, an investment boom gets out of hand. Maybe excessive money creation or reckless bank lending drives it, maybe it is simply a matter of irrational exuberance on the part of entrepreneurs. Whatever the reason, all that investment leads to the creation of too much capacity—of factories that cannot find markets, of office buildings that cannot find tenants. Since construction projects take time to complete, however, the boom can proceed for a while before its unsoundness becomes apparent. Eventually, however, reality strikes—investors go bust and investment spending collapses. The result is a slump whose depth is in proportion to the previous excesses. Moreover, that slump is part of the necessary healing process: The excess capacity gets worked off, prices and wages fall from their excessive boom levels, and only then is the economy ready to recover.

Here's the problem: As a matter of simple arithmetic, total spending in the economy is necessarily equal to total income (every sale is also a purchase, and vice versa). So if people decide to spend less on investment goods, doesn't that mean that they must be deciding to spend more on consumption goods—implying that an investment slump should always be accompanied by a corresponding consumption boom? And if so why should there be a rise in unemployment?

The hangover theory, then, turns out to be intellectually incoherent; nobody has managed to explain why bad investments in the past require the unemployment of good workers in the present. Yet the theory has powerful emotional appeal. Usually that appeal is strongest for conservatives, who can't stand the thought that positive action by governments (let alone—horrors!—printing money) can ever be a good idea. Some libertarians extol the Austrian theory, not because they have really thought that theory through, but because they feel the need for some prestigious alternative to the perceived statist implications of Keynesianism. And some people probably are attracted to Austrianism because they imagine that it devalues the intellectual pretensions of economics professors. But moderates and liberals are not immune to the theory's seductive charms—especially when it gives them a chance to lecture others on their failings.