I want to steer clear of critiquing the work of others but my comments on long odds seem to have evoked a torrent of emails about Nassim Taleb and his work on randomness and black swans. Let me start off by sketching the points on which we agree. I think that Taleb is absolutely right that we (in academic finance and model building) have become enamored with normal distributions when building models. The real world delivers far more jumps, surprises and asymmetric movements than can be justified by a normal distribution. I also believe that what Taleb is saying was said much better by Benoit Mandelbrot several decades ago, in his argument for power distributions (which allow for bigger jumps than the normal distribution). My book on strategic risk taking has an extended discussion of Mandelbrot's work.
Here is where I part ways with Taleb. While I agree that we are always susceptible to the unforeseen event (the black swan), I do not subscribe to his prescriptions. The first one (and I may be mistaken in this) is that planning, forecasting and valuation are useless since they will all be rendered to waste by the "black swan'' event. This is the equivalent of arguing that it is pointless planning and saving for retirement, since you may be hit by lightning tomorrow... logical, maybe, but not very sensible. The second one is that you can somehow make money off the fact that model builders have a normal distribution fixation.. Taleb argues that since models are built upon normal distributions, investors can make money by buying out of the money options and other investments that profit from big moves. I think that the mistake here is assuming that people who build models actually set market prices. If markets reflect reality rather than models, there should be no scope for profits.
Here is what I think. We have to make our best estimates of the future and value assets accordingly. We have to assume that there will be shocks to the system that we cannot anticipate and build an appropriate risk premium to reflect these risks. We cannot plan for the unforeseeable... and live our lives expecting black swans to show up..