We build a model with heterogeneous firms and banks to analyze how policy can affect the efficiency of credit allocation and long-term economic outcomes. When transitory demand or productivity shocks are small, conventional monetary policy can restore efficient bank lending and production by lowering interest rates. For moderately large shocks, however, conventional policy may hit the effective lower bound, necessitating unconventional policy such as regulatory forbearance towards banks to stabilize the economy. Aggressive unconventional policy runs the risk of introducing zombie lending and a “diabolical sorting”, whereby low-capitalization banks extend new credit or evergreen existing loans to low-productivity firms. In a dynamic setting, policy aimed at avoiding short-term recessions can be trapped into protracted excessive forbearance due to congestion externalities imposed by zombie lending on healthier firms. The resulting economic sclerosis transforms transitory shocks into phases of delayed recovery and potentially permanent output losses. Our model highlights the importance of maintaining a well-capitalized banking system to avoid such policy traps as not raising capital requirements upfront but raising them significantly upon the arrival of shocks can also backfire by encouraging zombie lending.