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This is idiotic. They crisis was caused by reckless banks who lent money to unqualified borrowers because the banks could get the garbage off their books by packaging and selling it as Triple-A investments. Take FNM, FRE, and mortgage securitization out of the equation and this never happens. Banks had the ability to shift risk to someone else so they didn't care about the risk involved in the reckless lending.
No Nobel Prize Economist's theory caused this mess. Taleb's position is laughable.
That's Taleb's whole point, mortgage securitization is the brainchild of portfolio theory.
We all know that lending some random douchebag you don't know $100k to buy a house would be really dumb. We just wouldn't do it.
But according to portfolio theory, if you pool your $100k with other investors, and then split the money between a large number of random douchebags, much of the risk disappears.
Portfolio theory enabled the most conservatively managed (AAA bonds only) pension funds to lend huge amounts of money to douchebags with no job prospects to buy overpriced houses they couldn't afford.