Politicians are always going to let bygones be bygones - for the very good reason that voters expect them to think and talk about the future, not the past.

BBC: The Bank of England, the chancellor, and the target

But there is another big objection to the pure form of nominal GDP targeting, as described by Mr Carney in his December speech - which is that it does not let bygones be bygones.

BBC: The Bank of England, the chancellor, and the target