The ability to imperfectly but robustly enumerate a set of alternatives manifests itself in many human activities. However, many cognitive models have fundamental difficulties with this task, which often leads to degenerate behavior. The primary source of this problem is the conflict between mechanisms of long-term reinforcement and the need for short-term inhibition of recent items. Our analysis of a pair of pervasive domains of human activity finds that the long-term reinforcement process is balanced by a short-term inhibition. We have implemented this empirical finding in a variation of the knowledge reinforcement equation of the ACT-R architecture. This new mechanism not only prevents degenerate behavior in memory retrieval, but also emerges as a source of the power law distribution observed in the environment, supporting the proposition that the power law distribution arises from the interaction of the environment and cognition itself.