1. The event is a surprise (to the observer). 2. The event has a major effect. 3. After the first recorded instance of the event, it is rationalized by hindsight, as if it could have been expected; that is, the relevant data were available but unaccounted for in risk mitigation programs. The same is true for the personal perception by individuals.
Thanksgiving is a black swan for the turkey but not for the butcher. Taleb is trying to solve the problem of how not to be a turkey, and prediction is insufficient for that problem, because errors of prediction will let the worst events through anyway. Rather one should evaluate how much worse things will be as an event grows. If problems grow faster than linearly, trouble will strike eventually.
