There are three problems with major disasters: small miscalculations of probabilities can have large effects on outcomes when dealing with large events; our reward structures do not encourage spending the time or the money to deal with low-probability disasters; the very complexity of modern life — including our transportation and communication systems, our economy and our social interactions — is directly implicated in the severity of catastrophes; in more complex systems, even small changes or perturbations can have disproportionate and unpredictable effects