The main problem is the difficulty the policy maker faces in distinguishing between objective and subjective uncertainty, and how to cope with the latter. Possible solutions to uncertainty are on the one hand to relax the assumption that a single probability number quantifies beliefs and assume that they can account on a set of them.
The policy makers then act according to the belief that minimizes the excepted loss. On the other hand the risk aversion of policy makers towards the two types of uncertainties is not the same. Allowing for the distinction in the attitude towards uncertainty allows us to evaluate their role and quantify their importance. As already stressed, the crises increased the concern for uncertainty.