theory of constraints (TOC), as a management approach, has been around for almost two decades, and its creator, Eliyahu M. Goldratt, has been applying the basic principles even longer than that. Consultants have been expending a lot of effort in helping their clients use TOC to effect real change?quantum improvements?in the performance of their organizations. Visionary people within client organizations have been trying to apply what they have learned about TOC toward the same end. For both groups, the results have been mixed. For every success, there have been more failures. (Failure can be defined as TOC producing ?underwhelming? results, being abandoned altogether, or the organization reverting to the way things were before the change.) The question is: Why?