Stuff happens...................

The lesson is that no amount of sophisticated statistical analysis is a match for the historical experience that "stuff happens".  At the heart of modern macroeconomics is the same illusion that uncertainty can be confined to the mathematical manipulation of known probability.  To understand and weather booms and slumps requires a different approach to thinking about uncertainty.

-Mervyn King,  The End of Alchemy:  Money, Banking, and the Future of the Global Economy