To understand the economy then is to comprehend how it is driven by the animal spirits. Just as Adam Smith's invisible hand is the keynote of classical economics, Keynes' animal spirits are the keynote to a different view of the economy — a view that explains the underlying instabilities of capitalism.

George Akerlof and Robert Shiller. Animal Spirits: How Human Psychology Drives the Economy, and Why It Matters for Global Capitalism, 2009, Preface