Curiously, many companies frequently bandied about by shareholder activists as prime examples of the effectiveness of the separation of roles tried it — and dropped it. These firms include I.B.M., Procter & Gamble, Home Depot, Boeing, Dell, General Motors, Time Warner and Walt Disney. If this governance structure was so universally priceless, why did the “try it, you’ll like it” experiments fail so quickly, with the very boards that had introduced such role separation recombining the leadership roles? Recent research on 309 companies that separated roles between 2002 and 2006 by Matthew Semadeni and Ryan Krause of Indiana University found that the financial performance of high-performing companies was often hurt by the separation. In fact, only 23 percent of S&P 500 firms have a truly independent director as chairman.

Some of the biggest corporate scandals in American history, from Enron to WorldCom to Computer Associates to Global Crossing, already had such separate roles in place and were celebrated for their overt good-governance models before they collapsed in criminal fraud. In fact, HealthSouth checked all the boxes that ISS cherishes and outearned 92 percent of the companies in its industry — just months before a series of former chief financial officers admitted to the huge accounting fraud there that put them and their flashy but self-righteous chief executive, Richard M. Scrushy, in prison.

Many times, in addition to confusion over responsibilities and voice, the separation of roles escalates palace intrigue. The former “independent chairman” of General Motors, Edward E. Whitacre Jr., previously a telecom executive, seized the chief executive job from the revered G.M. loyalist Fritz Henderson, who successfully led the firm out of bankruptcy, because Mr. Whitacre wanted the job for himself.

Shareholder activists frequently cite the separation of roles as the prevailing model in Europe, so thus, like fine European wines and Parisian fashion, it is presumed to be superior to any cowboy leadership of Yankee business enterprise. However, name your favorite European scandal and you’ll find they had this separation of roles in place.

The logic is that slowed decision making and balanced power will reduce risk and allow protection for minority interests. But business must encourage prudent, strategic risk taking. In the town square of villages in almost every nation, there is a statue celebrating not a board committee but a courageous individual leader.

It conjures up the old adage that ships are safest on shore, but that is not why they are built.

Jeffrey A. Sonnenfeld is senior associate dean for executive programs and a professor in the practice of management at the Yale School of Management.