Burt Malkiel's famous book, A Random Walk Down Wall Street, represents mainstream thinking in financial economics. It strongly supports the Efficient Markets Hypothesis and challenges much of behavioural finance. Many, many, MANY economists believed this paragraph from page 415 of his 2007 edition:
Hysteria seems especially out of place when people proclaim that the large losses triggered by derivatives could threaten the stability of the world financial system. While enormous leverage and extraordinary potential losses from derivatives will continue to receive banner headlines, a number of international study groups have concluded that a spreading worldwide financial crisis caused by derivatives is highly unlikely. Speculators who take large risks will continue to risk ruin, and some financial institutions --- even large ones --- will continue to fail. But a systematic undermining of world financial stability caused by derivatives trading does not deserve to be on the top of anyone's worry list. [emphasis added]
Oops. It looks as if "highly unlikely" refers to the very low odds of ever seeing a black swan. From Wikipaedia,
The Black Swan Theory (in Nassim Nicholas Taleb's version) concerns high-impact, hard-to-predict, and rare events beyond the realm of normal expectations. Unlike the philosophical "black swan problem", the "Black Swan Theory" (capitalized) refers only to events of large magnitude and consequence and their dominant role in history. "Black Swan" events are considered extreme outliers.