Myths of the theory of constraints and the clarification

The theory of constraints was proposed in the mid-1980s and has significant impact on the productivity improvement in manufacturing systems. While it is intuitive and easy to understand, its conclusions are mainly derived in deterministic settings or based on the first moment results. Since production systems are stochastic in general, some of its conclusions are not rigorous and have to be modified. In this study, we show that the process of ongoing improvement may lead to unfavorable outcomes and the throughput bottleneck should be planned on certain types of machines. Specifically, if a system has no bottleneck, every station will be a bottleneck. Furthermore, through capturing the dependence among stations, we show that improving the variability of a frontend machine in a production line can be more effective than improving the variability of a throughput bottleneck.