One day in the summer of 2011, Christine Richard arrived at the forty-second floor of a high-rise on Fifty-seventh Street in Manhattan to visit a hedge fund called Pershing Square Capital Management. Richard worked for a boutique research firm that identified “short”...

There was an unusual degree of consensus among economists about what would happen if Britain voted for Brexit in the referendum on June 23 last year. The language used by the International Monetary Fund was typical: It expressed fears of an “abrupt reaction,” adding...