shutterstock_125741561Tidjane Thiam, CEO of Credit Suisse, uttered the one word a bank chief should never say. No, it’s not of the four-letter variety, but it might as well be.

The word is “surprise.” Mr. Thaim stunned investment analysts by using it to describe his reaction to learning of the size of the bank’s trading book, something that apparently had escaped his notice until now.

Here’s how the New York Times reported it:

On a conference call with analysts on Wednesday, Mr. Thiam said the size of the positions on the bank’s trading book “was a surprise for a number of people and was not a widely known fact.” Top executives, including himself, became aware of them only in January, months after they first outlined a plan to refocus the company on less volatile businesses. (emphasis added)

Yes, that’s right. The CEO admitted he didn’t know what was in the trading book.

Surprise is a word no one wants to hear from a bank chief – not shareholders, not employees and definitely not regulators.

They all must be asking how, in the post-crisis era, it is possible for a bank CEO to be surprised about the trading book? Bank CEOs are supposed to be focused on risk management with a zeal bordering on obsession, supported by legions of analysts and snap-of-the-finger reporting technology. So Mr. Thiam’s comment suggests something is definitely amiss at Credit Suisse and it goes much deeper than bad quarterly earnings.

This is a reminder that a word choice can often reveal more than the speaker intended. Mr. Thaim might have intended to focus his remarks on the difficult trading environment and his plan to trim costs. But by using the word “surprise,” he instantly made the adequacy of the bank’s risk controls – and his abilities as a CEO – the dominant issues. Both are now big questions for the bank, and they won’t be resolved quickly.

He probably didn’t practice that answer with his communications team. (Or if he did, they should be fired straight away.) He could have said the positions were “no longer appropriate in the current environment” or “were outside of our acceptable risk range” – something that suggested he was managing the situation, not getting blindsided by it.

Bank CEOs can survive if they report a big loss on bad bet they at least knew about. Just ask Jamie Dimon. But admitting you didn’t know you had a big bet is harder for investors to accept.

Mr. Thiam has been at the helm less than a year, so investors might give him more time to straighten things out. But it’s missteps like this that could shorten his tenure.

If that happens he shouldn’t be surprised.