Unusually low interest rates currently keep the carrying costs of these debts modest, and make it seem as if the day of reckoning is far off. Sadly, debt can be worked off only slowly, while rates can rise suddenly. Such a rise, if sustained, would be extremely painful for the national budgets of many countries, including those struggling in Europe. Research on sovereign default shows that markets also seldom anticipate problems in advance. By the time they lose confidence, it is too late: the option to tighten from a position of strength has evaporated.