It often goes unmentioned, but McKinsey has indeed offered some of the worst advice in the annals of business. Enron? Check. Time Warner’s merger with AOL? Check. General Motors’s poor strategy against the Japanese automakers? Check. It told AT&T in 1980 that it expected the market for cellphones in the United States in 2000 would amount to only 900,000 subscribers. It turned out to be 109 million. The list goes on.