Summary:
Forecasting is extremely difficult and usually little better than guessing. Most experts in social sciences, especially finance and economics, overrate themselves, proclaiming abilities they simply don't have (he uses the word "fraudster" many times). Risk analysis, and indeed all statistical work that relies on Gaussian assumptions, doesn't work because Gaussian assumptions don't hold in most real world situations, which are subject to "unknown unknowns". He cites the example of a casino which used mathematics to control its losses to gamblers but still lost a lot of money when an irreplaceable performer in their main show was maimed by a tiger, and when the owner's daughter was kidnapped. it nearly lost its licence when an irresponsible employee hid a bunch of tax returns instead of filing them. These, of course, are the black swans of the title.