Although lean popularity is rapidly growing, its implementation is far from problem free and companies may experience difficulties sustaining long term success. In this paper, it is argued that the human behaviour, affected by the implementation of both hard (defined as technical and analytical tools) and soft lean practices (concerning people and relations), plays a key role in achieving long-term superior performance. Through a single case research, the relationships between lean practices implementation, human behaviour and operational performance are explored. From the analysis a new construct emerged, namely “Individual characteristics”. As a result, an alternative research model for further statistical testing including individual behaviour as mediating variable and individual characteristics as moderating variable has been built.