Greece is in danger of defaulting on its debt. Because Greece uses the Euro, Greece's danger is, in part, passed on to other countries using the same currency. The big problem with Europe's strategy of strength in numbers, is that it causes the corresponding weakness of inflexibility.
To give a strange example: supposing my friends and I decided to unify our bodies into one. The advantages would include the free flow of blood across individual boundaries. If one friend is short of a nutrient, another can make a contribution. But what if one friend gets an infection? Because we have got rid of our individual skins, we no longer have control over how rapidly an illness affects us all. One friend cannot run to the shops for medicine while the other gets some rest.
And this is the climate of Europe for the moment. Whether Greece's illness becomes Ireland's, and then Portugal's, and leaks across Europe, remains to be seen. What is certain, is that it is hard for stronger economic powers, such as Germany, to avoid being bound up in their neighbour's struggle; Chancellor Merkel may appear reluctant to commit to too much financial help for Greece, but, if part of a body is infected, the rest of the body is already committed to a fight.