Tsipras should tread lightly

"It's a personal victory for Prime Minister Tsipras, and it also means a clear negotiating position for him," Bastian said in an interview with DW. "But now he has to be careful not to over-interpret this victory, but instead be sure to balance the interests of his country and its citizens with the interests of his party."

From Bastian's perspective, he said the pollsters have ample reason to feel embarrassed after incorrectly predicting a neck-and-neck outcome for the referendum. "No one on either side expected such a clear outcome. This is somewhat of a political sensation, a landslide. It's an even stronger result than Syriza received in the parliamentary vote on January 25."

A vote of anger

Many observers, however, question whether voters made the right decision. Ahead of the vote, 246 Greek economics professors warned in an open letter of the massively destructive consequences that could follow a "Grexit" - to no avail.

Asked whether ideology had triumphed over common sense, Bastian remained skeptical. "Most people voted in anger," he said. "They'd been through so much, unemployment and loss of real income, threats to their pensions and reductions in the availability of medical care."

"And then there was European Commission President Jean-Claude Juncker or the president of the European Parliament, Martin Schulz, who so clearly interfered with the referendum, embittering many Greeks. Many felt that to be inappropriate and so the 'No' camp was strengthened. That shot really backfired."

New billions due

On July 20, Greece is due to repay 3.5 billion euros in government bonds to the European Central Bank (ECB). This will not work. Then the ECB will have to officially declare Greece insolvent, which will inevitably lead to the bank cutting Athens off from emergency loans under its Emergency Liquidity Assistance (ELA) program. This will block Greece from its supply of fresh euros and would effectively amount to a knockout for Greece without anyone having to kick the country out of the common currency.

Bastian told DW he thought very few Greeks were actually aware of these possible consequences. "Their reasons for voting were different. These consequences weren't even on their radar. It means Tsipras must make clear to his people that there are only 15 days left until the cutoff date on July 20. By then there needs to not only be negotiations but also an agreement that includes a bridge loan. Otherwise Greece will be insolvent vis à vis a second creditor after the International Monetary Fund."

More humility

Of course Bastian, an economic expert, knows that Tsipras and his outgoing finance minister, Yanis Varoufakis, were betting on their country's importance in the European Union, in NATO and in the OECD - memberships that would always grant them chances that would not be permitted to a normal debtor.

Should it come to negotiations over a third aid package for Greece, Bastian has called for more humility from both sides. "Not only from Greece but also from the side of the European creditors. They have to accept that the result of the referendum does not leave room for interpretation. The European side must now regroup and determine a way to offer some flexibility - maybe even a Plan B."