Myron Scholes

A bank needs models to measure risk. The problem, however, is that any one bank can measure its risk, but it also has to know what the risk taken by other banks in the system happens to be at any particular moment.

Keynesian modelling relies on marginal propensity to consume and marginal propensity to invest. The idea that if we give more money to the poor, they have a propensity to consume that's much higher than the wealthy, though I wish they would talk to my wife about that; she seems to have a propensity to consume.