I heard an interesting analysis of the Euro, on my radio the other day.
It effectively has different values in different countries. So to Germany it is cheap, and they are doing well, whereas to Greece it is expensive, and too rich for their economy.
The 'One size fits all' ethos/ideal, of the Euro, never has, and never will work. When the countries involved are so economically disparate.
When a packet of cigarettes, or a bottle of beer are the same price in all the countries involved, and the wages are the same. Then, and only then, will a common currency work