According to Krugman, humans don't ever save. We either invest in the market, or we spend on consumer goods. There is no allowance for the thinking human, who sees both investment and consumption as poor uses for their capital, and thus, he can't see the recession coming.

I guess he thinks he's the only thinking human in the economy, and the rest of us are just robots following the Keynesian script.

What a glaring error.

You do realize that in modern economies, people don't save by burying their money in the backyard anymore? People "save" by putting money in the bank, which is investment spending.