Lean has established itself as the primordial approach to obtain operational excellence. Its simple and intuitive techniques focus on reducing lead time through continuous improvement, involving all levels of employees in the organization. However, the rate of successful implementations has remained low. This paper contributes to the understanding of continuous improvement in a Lean context, by analyzing a database of almost 10.000 improvement actions, from 85 companies, covering the time frame 2010–2018. It discusses categories of actions, their impact and cost, as well as key characteristics of the companies. It proposes an objective criterion to identify “success” and “failure” in Lean implementation and tries to link these to operational results. It is probably the first time an analysis of this magnitude on the subject has been performed.