Jeffrey Kindler, the CEO of Pfizer, the world's largest drug-maker, has unexpectedly quit, citing the "incredibly demanding" nature of his job. Although Pfizer suffered mixed fortunes during Kindler's four-plus year tenure and its stock price has slipped by 35 percent, the sudden nature of Kindler's departure has commentators speculating what prompted his exit:

He was exhausted: Running Pfizer "doesn't sound like fun," says Tracy Corrigan at The Daily Telegraph, and "Kindler, to his credit, has been honest enough to say so." Saying his job was "extremely demanding" on a personal level is as close to straight talk as any "statement rewritten by corporate PR advisers can be." I call that a "touchingly human and unpretentious" move.
"Pfizer boss admits exhaustion and quits. How very refreshing"

He bet on the wrong strategy: Kindler made the "brave wager" that Pfizer should "eschew big acquisitions and bet on its research laboratories," says Matthew Herper at Forbes. But "the strategy failed." Pfizer then bought rival Wyeth for $68 billion, but the combined company still hasn't come up with a new drug to rock the market — specifically, a replacement for cholesterol drug Lipitor, whose patent expires next year. Out of ideas, Kindler handed over the reins to someone else.
"Pfizer CEO retires suddenly"

This incompetent CEO was shown the door: Kindler "was almost certainly pushed out," says Douglas A. McIntyre at 24/7 Wall St, given the fact that his successor, Ian C. Read, was promoted from within (a questionable choice; Read also helped oversee the "botched integration of Wyeth"). Now that some corporations are seeing a surge in earnings, it seems boards think they can "afford to replace incompetent CEOs." Expect Kindler to be the first of many.
"Pfizer CEO gone, who is next?"