Even some of the smartest guys in the room got this one wrong.
The billionaire hedge fund manager Leon Cooperman told an audience of Wall Street insiders on Wednesday that there was a 70 percent probability that Britain would stay inside the European Union. "I don't worry about Brexit," he added.
Two weeks earlier, George Soros, who became known as the man who broke the Bank of England with a bet against the British pound in 1992, said he was "confident that as we get closer to the Brexit vote, the 'remain' camp is getting stronger."
"Markets are not always right, but in this case I agree with them," Mr. Soros added.
Then on Thursday, the British electorate voted to leave. The reaction in markets was swift and violent: Stocks around the world went into free fall, the British pound sank to a more than 30-year low against the dollar, and central banks pledged to provide emergency help.
Ben Hunt of Salient Partners, went as far as to call it a "Bear Stearns moment," evoking the investment firm whose collapse in March 2008 was a prelude to the financial chaos that September.