Mispriced risk. The global economic contagion was created by mispricing (read, underestimating) risk. And apparently this is all a Canadian-educated Chinese mathematician's fault (way to externalize blame!)
So, for me the question is how do governments create policy regimes that encourage proper risk-management? Obviously, powerful governments have a credible commitment problem since the costs of letting a financial institution dissolve in the face of risk bets gone bad are untenable. But, as the parable of the Gaussian Copula Function tells us, there is little incentive for financial institutions to moderate or to be cautious. So, our outcome seems doomed to be Pareto sub-optimal.
Even more concerning is industry and governments proclivity toward over-compensation. When this financial mess bottoms out and we recommence our dogged climb toward ever-increasing prosperity, there will probably be a heck of a lot of regulation concerning the ways in which CMOs and credit default swaps can be created, rated, bought, and sold. But, the underlying cause of financial blow up was not crazy mortgage-backed derivatives per se, rather risk mis-management stemmed from a deeply human tendency to discount "outliers" and treat events that occur under a certain threshold of probability as practically impossible. And, until risk calculations take correlation seriously, financial firms in their legal obligation to produce the greatest returns for shareholders will continue to find ways to delude themselves and their clients into believing that you can make lots of money without taking on any risk.