The economic crash was so obvious -- in hindsight.

Big banks such as Citigroup (NYSE: C) and Bank of America (NYSE: BAC) were lending enormous sums of money to borrowers who stood no chance of paying it back. Housing prices were so clearly overvalued. Consumers were keeping spending up only by borrowing unsustainable amounts. How could we have missed it?

Yet so many of us -- even (or especially) the experts -- did.

Earlier in December, I sat down for a wide-ranging interview with famed Wharton finance professor Jeremy Siegel. Here's what he had to say when I asked him why so many experts missed the crash.

What do you think? Share your thoughts below.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.