In the end, the question remains: why were investors willing, eager even, to invest in such complex products they must have known they did not fully understand? Why did some financial institutions allow their business model to become so dependent on particular forms of market funding? Yes, the complexity obscured risk. But investors and institutions were not deterred by that.
The simple point, surely, was that there was too much optimism combined with too much leverage. That is neither new, nor particularly complicated. I am prepared to assert that it will, periodically, recur. Policy makers across a range of endeavours will need to keep that very much in view in the future.