The Bank of Japan did exactly what it said it would do: nothing. Yet traders were stunned.

The market churn after the Jan. 18 decision to keep policy unchanged, something expected by almost every economist surveyed, might seem a little odd. Blindsided in December by Gov. Haruhiko Kuroda’s yield-curve control tweak, some observers had begun talking themselves into believing that not just further adjustments were possible, but that he was set to wholesale dismantle his decade-long easing program.

Some of this was wishful thinking; others were hoping to force the BOJ’s hand. Nonetheless, Kuroda seemed bemused, as were many domestic observers puzzled by expectations that the central bank would not just tweak, but soon shift to a full-on tightening just as its inflation target comes tantalizingly within reach and crucially before wages have a chance to lock that change in.