The Unknown Unknowns

The Gulf Oil Leak—Posner - The Becker-Posner Blog: "It would be nice to be able to draw up a complete list of disaster possibilities, rank them by expected cost, decide how much we want to spend on preventing each one, and proceed down the list until the total cost of prevention equals the total expected cost averted. But that isn't feasible. Many of the probabilities are unknown. The consequences are unknown. The costs of prevention and remediation are unknown"