If the Fed were to try to keep market rates persistently too high, relative to the equilibrium rate, the economy would slow (perhaps falling into recession), because capital investments (and other long-lived purchases, like consumer durables) are unattractive when the cost of borrowing set by the Fed exceeds the potential return on those investments. Similarly, if the Fed were to push market rates too low, below the levels consistent with the equilibrium rate, the economy would eventually overheat, leading to inflation—also an unsustainable and undesirable situation. The bottom line is that the state of the economy, not the Fed, ultimately determines the real rate of return attainable by savers and investors. The Fed influences market rates but not in an unconstrained way; if it seeks a healthy economy, then it must try to push market rates toward levels consistent with the underlying equilibrium rate.