In his Theory of Constraints, Dr. Eliyahu Goldratt provides a methodology for identifying and eliminating constraints. It is referred to as the Five Focusing Steps and can also be used to deal with bottlenecks (constraints) identified with the Kanban method. A bottleneck can be easily found in a Kanban system by observing the Kanban board. Once you observe that at least two neighbouring columns are consistently filled to their WIP limit, the last of those columns will likely contain the bottleneck for the entire system. Identifying the constraint is the first step of the Five Focusing Steps, so what are the next ones?
You should initially focus on making the most out of your constraint, i.e., maximising the throughput of the workflow step that contains the bottleneck without any additional investments to increase the capacity or resources available for that workflow stage. This step is crucial since the constraint's throughput dictates the system's throughput. Hence, if the constraint is not squeezed to its fullest, the system will produce less than its theoretical limits. This step of the Five Focusing Steps is called “exploit the constraint”.
After that, we shall “subordinate everything else to the constraint”. In a Kanban system, we should ensure that no other stage of the workflow is allowed to have higher throughput than the constraint. That step comes naturally in Kanban since consistent use of WIP limits in all columns representing in-progress workflow stages naturally will subordinate the other stages to the constraint.
Only then can we proceed to “elevate the constraint”, which means investing in increasing the constraint's throughput. Keep in mind that the constraint might move to a different part of your workflow before you have reached this step, and instead of “elevating”, it might be much more appropriate to start all over from step 1 of the Five Focusing Steps but for the new constraint.
Even if the constraint was in the same place by the time you reached the fourth step, it will finally move elsewhere if you continue elevating it. Therefore, the last step of the Five Focusing Steps is repeating all previous steps in the same order.