"There is a way... which comes from economics and social science. It was developed by... Frank Knight, and Keynes used this... The distinction between risk and uncertainty... [R]isk is about things... we... understand... known unknowns, to use Donald Rumsfeld's... great phrase... [something] we can put numbers on, things within... circumscribed situations... A lot of medicine is like this... repetition, a lot of data. ...[I]nsurance is like this ...We know roughly what the chances are, and we can talk about the numbers. Uncertainty is when... we don't know the numbers, or... deeper... we don't even know... the problem... the options... the possible outcomes..."