For Greece, did entry into the Euro allow too easy access to too much cheap credit, so that the private sector went into too much debt ?
It looks that way from this BBC article on ”What really caused the eurozone crisis?”

As Germany was keeping a lid on wages and become a net exporter, Italian and Spanish wages went up. They became uncompetitive, so their economies stalled, as the global financial crisis hit, where the governments wanted to increase their government level borrowing and stimulation.