If history is any guide, running up debt is not advisable. But making sense of the economy is a constant challenge because it keeps changing, and the past doesn’t tell us much about the future. Technology evolves, trade increases, and more people achieve higher educational levels; the nature of work changes, as do the factors that influence unemployment and inflation and interest rates. It is now conventional wisdom that things once seen as big risks—excessive debt and inflation—are no longer as much of a concern.