One thing about Summers is that he is slippery. He almost always includes little caveats in his writing even though his prescriptions are made with 100% certainty.
The piece which kicked off the war on expansionary fiscal policy contained this line:
He gave 1/3 odds to each of 3 scenarios, and precisely none of them actually happened. Still everyone decided Larry Was Right and he got what he wanted - a curtailing of the nice things the country briefly had.