Elite firms’ notorious ‘revolving door’ culture isn’t arbitrary but a rational way to signal talent and boost profits, a new study finds. Why do the world’s most prestigious firms—such as McKinsey, Goldman Sachs and other elite consulting giants, investment banks, and law practices—hire the brightest talents, train them intensively, and then, after a few years, send many of them packing? A recent study in the American Economic Review concludes that so-called adverse selection is not a flaw but r...