Behavioural System Dynamics: Conceptual Integration of Critical Bias Variables into Circular Economy Stakeholder Phases

System Dynamics (SD) is a powerful lever to understand the influence of biases on sustainable decisions. This paper describes modelling methods that shed light on the level of rationality of stakeholders in the Circular Economy (CE). The main aim of the paper is to explore how complex systems, such as mental models of consumers in the CE, can be evaluated with Behavioural system dynamics (BehSD). This is done using a causal loop (CLD) and stock and flow diagrams (SFD). The model builds on the need to improve sustainable activities by better understanding biases. The paper concludes with a simulation using pseudo-random data to showcase that efforts to reduce biases can influence consumer behaviour effectively. It is important to note that rebound effects and policy decisions are significant amongst many other external influences that need further evaluation.