" Finally, policymakers had to weigh what might happen if Greece, after a default, also abandoned the euro and returned to its own currency. One reason to do so would be to regain monetary policy independence, which might help the Greek government respond to the economic crash that was likely to follow a default. But if Greece left the euro, fears that other countries might follow would no doubt increase. Even the possibility that the eurozone might break apart would inflict damage. For example, bank depositors in a country thought to be at risk of leaving the euro would worry that their euro-denominated deposits might be forcibly converted to the new, and presumably less valuable, national currency. To avoid that risk, depositors might withdraw their euros from their own country’s banks in favor of, say, German banks (which, in an era of cross-border branching, might simply mean walking a block down the street or clicking on a bank’s website). These withdrawals could quickly degenerate into a full-fledged run on the suspect country’s banks. For these reasons, finance ministers and especially central bank governors in Europe generally, if grudgingly, concluded that they would have to assist Greece. ECB president Jean-Claude Trichet, who had decried the Lehman failure, was particularly adamant on this point and sought to persuade other European policymakers. "
― Ben S. Bernanke , The Courage to Act: A Memoir of a Crisis and Its Aftermath