Just days before the Bank of Japan stunned financial markets with its radical adoption of negative interest rates, members of the central bank's own policy board had also been taken by surprise by the move.
Most of the nine board members were only told of the scheme in the week leading up to last Friday's rate review, according to interviews with more than a dozen officials familiar with the deliberations.
The startling speed and secrecy with which such a major policy shift was executed suggest its intent was more about delivering a shock to markets that would weaken the yen, than about maximising the stimulative impact of further easing.
That would be in keeping with the single-minded style of central bank Governor Haruhiko Kuroda, people who know him well or have worked with him say, but could risk entrenching divisions between BOJ policymakers.
"If you're a board member, you're told about the plan at the last minute," said a former board member, speaking on condition of anonymity. "It's hard to argue against it or draft a counter proposal when there's so little time left."
The BOJ declined to comment on the decision-making process.
Kuroda had been saying for months that taking rates below zero was not a timely option, a position he had repeated as recently as Jan. 21.