“If you know that the stock market can crash, as it did in 1987, then such an event is not a Black Swan.”
This contradicts other things Taleb has said. But Taleb doesn’t seem to fear contradicting himself.
A Black Swan in Taleb’s metaphor is an event (or thing) that cannot be predicted from the existing data set. It is an “unknown unknown” (apparently former Defense Secretary Donald Rumsfeld isn’t the only one who likes this phrase). Europeans had only ever seen white swans. “White” was one of the definitions of “swan.” Then black swans turned up in Australia. Nobody could have predicted!
An unanticipated market crash then would be more a “gray swan”? “A gray swan concerns modelable extreme events.” You don’t know when it’s going to happen but, as it’s happened in the past, it’s within the realm of possibility and you can take steps to protect yourself (or take advantage).
source: The Black Swan: the impact of the highly improbable by Nassim Nicholas Taleb