[영문]AbstractEconomists have recently argued recessions play a useful role in fostering growth. Yet a major source of growth, Rqqqamp;D, is procyclical. This paper argues one reason for procyclical Rqqqamp;D is a dynamic externality inherent in Rqqqamp;D that makes entrepreneurs short-sighted and concentrate their innovation in booms, even when it is optimal to concentrate it in recessions. Additional forces may imply that procyclical Rqqqamp;D is desirable, but equilibrium Rqqqamp;D is likely to be too procyclical, and macroeconomic shocks are likely to have overly persistent effects on output and make growth more costly than in the absence of such shocks.