Unlike Adam Smith, the Swedish interest-rate expert never made it to the face of a banknote. In 1898, Wicksell shared the idea that inflation and economic instability stem from an imbalance: It occurs when market interest rates (set by the Fed and by banks) are out of sync with “the natural rate of interest.” The “natural” rate, Wicksell proposed, is the level of return investors get from investing in the economy as a whole (for instance via stocks) as opposed to the interest they might get from cash deposits or bonds. The U.S. economy is so strong that its natural rate is far above its official rates, which is why interest on American debt is relatively low given its size. “The U.S. economy can therefore be seen, in some ways, as both a gainer and a victim of its own success,” the team concludes.