Take Lloyds Banking Group. One would have thought after the travails of the past three years that there would be nothing left to surprise it and there would be a contingency plan for everything. But that is not as it has turned out.
Two months ago, the bank announced that Antonio Horta-Osorio, the chief executive who only took the job in March, was suffering from extreme fatigue and had to take time off.
That news on its own would have been difficult to handle, but it could surely have been better done. Since the initial announcement, shares have drifted lower - and they were in a bad way to start with. Worse, the indisposition of the chief executive has brought the knives out everywhere. The board may initially have been saying he would be away only temporarily, but the grapevine was delivering a quite different series of messages and it quickly became obvious that not all his senior colleagues were sympathetic to his plight.
This mischief-making eroded the credibility of the basic company story - that he was away for a few weeks but would soon be back. That in turn has created an atmosphere where the web has been flooded with blogs and posts saying how awful the culture is within Lloyds. This has fuelled stock market doubts that Lloyds will be able in any reasonable time span to sort itself out.
At a private dinner of FTSE chairmen recently, I asked the assembled throng how they as chairmen would have coped with a chief executive who they thought was heading for that kind of breakdown.
It unleashed a flood of black humour and gruesome anecdotes of past disasters mostly concealed from shareholders at the time. But what they did say, though often accepting they had not always been sufficiently decisive themselves, is that boards should plan on the basis that the ill chief executive will never return. To hope that he will be back in a few months risks making the business a hostage to fortune.
This is why Horta-Osorio's misfortune should have been better handled.
Anthony Hilton is City commentator on London's Evening Standard