This means that the credibility of monetary policy cannot be based on a central bank locking itself in by means of a specific irrevocable commitment. The possibility of such locking in of the central bank features prominently in analytical debate outside the central banking community, but it is probably an illusion, a will-o’-the-wisp?
(Currency board regimes being a separate regime altogether, and I do not think we are generally looking for last resort regimes.) All this is not a problem for the ECB in particular. It is a reality for all central banks operating in market economies.