And even if you can keep track of those differences, it's even harder to re-check the model's ground truth to determine whether the underlying factors have changed. That's how we got into so much trouble with #CollateralizedDebtObligations, which were supposed to be "risk-free" mortgage derivatives that could be safely insured and invested in.

20/

A quick refresher: Obama inherited the #GreatFinancialCrisis, a massive global asset crash that followed from a decade of real-estate and derivatives deregulation that saw the world's largest banks issuing mortgages they knew would fail, and then placing massive bets on "#CollateralizedDebtObligations" that were supposed to offset the risk.

5/