The economic framework they had in mind, known as the optimum currency area theory, predicts that the creation of a common monetary area becomes more costly the more the participating countries experience idiosyncratic shocks, in terms of size, nature and frequency, and the more varied their responses to such shocks are.
While asymmetric shocks and adjustment mechanisms have to be recognised as realities, they also have to be seen in a more general framework, within which all gains from Stage  2  BIS Review 20/2002  Three of EMU are taken into account. These gains are sizeable.