I don't know where this graph came from originally, so I'll credit Troktiko, where I saw the photo in the first place.
People around the interwebs seem to be taking this graph as evidence that Greece's Socialists are to blame for our huge mountain of debt. While I have endless sympathy for this sentiment, that is the wrong way to read the graph.
You see the Socialists actually paid off a good deal of our debt under Simitis and the Conservatives added to it (even above the purely cyclical effect) under Karamanlis Jr.
What actually happened was that the gravy train only stopped on three occasions: under dictatorship, during Papandreou's last (read: senile) days, and under Eurozone convergence. The three situations have one thing in common: the Greek people were unable to influence fiscal policy through clientilist politics either because no-one was listening, or because the people in charge were answering to a higher power.