The emergence of the explicit need for shared understanding as an underpinning flow in lean construction has generated some debate and exposed a need to provide a better explanation. Following an investigation comprising of a total of 27 interviews and several workshops, the data identifies and connects the relationship between inappropriate understanding and constraints to flow - represented through a conceptual model. The research further identified that introducing lean construction concepts associated with the Last Planner System caused the participants to realise the importance of a shared understanding when previously they had not raised it as a source of constraint or problem. The research concludes that a shared understanding is critical to the social aspects of a sociotechnical system and needs to be precise and project specific to achieve the desired outcomes. In this way, a shared understanding can be considered to be the equivalent of a machine code in an operating system - if the understanding breaks down then so does the project delivery system.