The politically and legally complicated character of the EU Eastern Enlargement heavily influenced the conflict between the legal and economic rationality underlying the construction of the EMR-II. This makes the ERM-II vulnerable to currency crises and creates conditions for a widespread currency and asset substitution in the accession countries. As a result, the required participation of all accession countries in the ERM-II imposes unnecessary costs on the whole enlargement process. The costs could be avoided if the EU adopted a more flexible approach to the enlargement of its monetary union, allowing for an individual path of adopting the euro in each accession country depending on the country's economic conditions.