Over the last three decades, there has been a vogue in manufacturing, and increasingly in services organisations to implement Lean. However, in many cases these journeys have not been as successful or sustainable as their architects had planned. The question is why have the results been worse than planned and have organisations got their implementation approach wrong? This paper considers this question and finds that the reason is largely due to the ‘easy’ results-oriented and tools-only approach of the organisations involved. It explores why this approach does not work using a critical-realist method in a longitudinal case organisation, based in Wales that has taken a different evolutionary approach and ultimately received Shingo Prize recognition. Its approach is based on principles-led behaviours, systems, and cultural change. This approach appears to be more successful and early indications are that it is more sustainable. The paper contributes to both the academic and practitioner communities by presenting a theoretical stage model and evolutionary framework of the development that the case company undertook as well as a discussion of how to overcome two barriers to successful Lean implementation. We therefore demonstrate how one can move beyond the common tool-based approach which has attracted the majority of criticism in the academic literature.