"Too much debt is always dangerous," write Paul Krugman and Robin Wells. "It’s dangerous when a government borrows heavily from foreigners—but it’s equally dangerous when a government borrows heavily from its own citizens. It’s dangerous, too, when the private sector borrows heavily, whether from foreigners or from itself—for banks are basically institutions that borrow from their depositors, then make loans to others, and banking crises are among the most devastating shocks an economy can face."