Just like other central banks, the European Central Bank is finding interest-rate guidance something of a challenge. Despite the introduction in July of a pledge to hold rates at current or lower levels for an "extended period," markets have steadily raised their expectations of a eurozone rate increase.

For some, that is because the ECB's guidance is too vague. But President Mario Draghi on Thursday said the ECB was sticking with its current guidance formulation. It is right to do so.