At this point, however, the evidence practically screams hysteresis. Even countries that seem to have largely recovered from the crisis, like the United States, are far poorer than precrisis projections suggested they would be at this point. And a new paper by Mr. Summers and Antonio Fatás, in addition to supporting other economists’ conclusion that the crisis seems to have done enormous long-run damage, shows that the downgrading of nations’ long-run prospects is strongly correlated with the amount of austerity they imposed.

What this suggests is that the turn to austerity had truly catastrophic effects, going far beyond the jobs and income lost in the first few years. In fact, the long-run damage suggested by the Fatás-Summers estimates is easily big enough to make austerity a self-defeating policy even in purely fiscal terms: Governments that slashed spending in the face of depression hurt their economies, and hence their future tax receipts, so much that even their debt will end up higher than it would have been without the cuts.

And the bitter irony of the story is that this catastrophic policy was undertaken in the name of long-run responsibility, that those who protested against the wrong turn were dismissed as feckless.

There are a few obvious lessons from this debacle. “All the important people say so” is not, it turns out, a good way to decide on policy; groupthink is no substitute for clear analysis. Also, calling for sacrifice (by other people, of course) doesn’t mean you’re tough-minded.

But will these lessons sink in? Past economic troubles, like the stagflation of the 1970s, led to widespread reconsideration of economic orthodoxy. But one striking aspect of the past few years has been how few people are willing to admit having been wrong about anything. It seems all too possible that the Very Serious People who cheered on disastrous policies will learn nothing from the experience. And that is, in its own way, as scary as the economic outlook.