black swan
n.— Note: Probably related to the theories of philosopher Karl Popper. «Finance is about numbers, and some numerical analysis will always be needed to see trends and plan investment strategies. But there are limits to numerical jugglery, and this is the underlying message of the current round of financial turmoil. Any amount of historical data fed into computers will not help economists and traders have a perfect understanding of the future. Financial alchemy will often create dust rather than gold. Rare events—call them black swans or fat tails—can make incredibly smart types look like fools.» —“The rise and fall of conceit” livemint Mar. 19, 2008. (source: Double-Tongued Dictionary)