Drowning in red ink, Greece has nowhere to turn to revive the economic growth that might put its debt on a sustainable trajectory, reassure angry foreign creditors and offer hope to its recession-weary citizens. Instead, the country finds itself in a vicious circle—a death spiral, some would say—in which it is borrowing ever more to keep up on its existing debts, crushing growth in the process and thereby worsening its all-important ratio of debt-to-gross domestic product. Springing the debt trap would not be a miracle cure either: a manageable level of borrowing is a necessary but not a sufficient condition...