Euros

I continue to be puzzled by the Euro and the fact that so many different economies have been prepared to share the same currency when their underlying economic strengths are so different. Take for example Germany and Greece whose economies are poles apart. At the present time the Pound to Euro exchange rate is very favourable. One pound Sterling buys about 1.33 Euros. Greece has said today it will not default on its loans,but how will it pay its debts?