Nothing defines the chief executive’s tenure as the manner and timing of their departure. With Josef Ackermann stepping down last month after a decade at Deutsche Bank, the obvious question for some of his peers is how to judge when it is time for them to go.

In the past few weeks, four of Ackermann's longer-standing counterparts have no doubt been mulling this question. Lloyd Blankfein at Goldman Sachs has just gone through his sixth anniversary as chief executive, and last week he batted away stubborn speculation about his future by joking he wanted to live to 117 (he's 57 now), and would probably "die at his desk".