From a New York Times profile of Roubini….

The dismal science, it seems, is an optimistic profession. Many economists, Roubini among them, argue that some of the optimism is built into the very machinery, the mathematics, of modern economic theory. Econometric models typically rely on the assumption that the near future is likely to be similar to the recent past, and thus it is rare that the models anticipate breaks in the economy. And if the models can’t foresee a relatively minor break like a recession, they have even more trouble modeling and predicting a major rupture like a full-blown financial crisis. Only a handful of 20th-century economists have even bothered to study financial panics. (The most notable example is probably the late economist Hyman Minksy, of whom Roubini is an avid reader.) “These are things most economists barely understand,” Roubini told me. “We’re in uncharted territory where standard economic theory isn’t helpful.”

I am not a big fan of Roubini, but this a good explanation of the fundamental problem of economics.