Today's world is characterized by volatility and uncertainty. Cooperation is needed to survive in this harsh business climate. Cooperation in supply chains are practiced and well known but in today's tough and volatile environment it is simply not enough. Wastes and unnecessary processes have to be eliminated to secure a competitive advantage. Incorporating lean in supply chains get more and more attention and embrace in the modern literature and media. Lean implemented in supply chains is praised to create a proactive supply chain that successfully eliminate waste and create efficiency. In the thesis the negative aspects, the angle that is very seldom described in the literature, of incorporating lean in supply chain is researched. I will view lean from the management perspective and research the negative aspects, their cause and impact on the entire supply chain. Being aware of the criticism of lean from the employee and society perspective this research serves to find if lean from the management perspective is a flawless story. To achieve the aim of this thesis I conducted a survey research where 100 supply chain executives from different countries, different industries and of different designations within supply chain management were asked to share their lean experience. The summary of my research show that lean incorporated in supply chains is not only a sunshine story. I can conclude problems, even a mismatch, with the lean concept incorporated in supply chains- the time sensibility lean brings. In my research it became obvious that lean supply chains are very sensitive to delays and that the consequences of the delays will strike very hard - hence the lean supply chain can also be seen as more vulnerable and fragile compared to ordinary supply chains. There is no question about the fact that any company, any network of companies or a supply chain for that matter, are better off without delays. A delay will always be negative. In a lean environment, where time aspects such as Just-In-Time and a pull scenario are present, a delay will immediately ruin the entire execution and the consequences will naturally spread in the supply chain. In today's volatile and ever changing world I believe that leanness in supply chains are indeed needed but to an extent where the time factors are viewed realistically in order to avoid drastic consequences. My conclusion is that supply chains should be realistically lean, bearing the time factors of lean in mind, to avoid being mean. I encourage every supply chain to identify their lean level in order to avoid a mean result.