Two weeks after Washington and Tokyo mounted an unprecedented joint effort to arrest the yen's slide, the currency has quietly surrendered half its gains, drifting back above 159 to the dollar. The episode illuminates a perennial tension in economic governance: the power of coordinated policy to startle markets, and its inability to repeal the deeper arithmetic of yield differentials and capital flows. As long as American assets offer investors nearly two percentage points more in return than their Japanese equivalents, the logic of the carry trade will reassert itself with quiet persistence.