The Plan-Do-Check-Act (PDCA) cycle is presented as the most fundamental framework for lean manufacturing and any organizational improvement process. All other lean tools are considered secondary to this core methodology. The primary reason for the failure of most lean projects in the Western world is not a deficiency in specific tools, but a widespread neglect of the PDCA cycle itself. While project managers often proficiently execute the "Plan" and "Do" stages, the "Check" and "Act" phases are frequently overlooked or deliberately ignored.