Sustainability represents a system attribute that is widely investigated in many disciplines. System dynamics is mostly used for modelling specific issues. Not only can this methodology be used for this purpose, it can also be applied for the identification of behavioural stereotypes and consequent designation of variables that shape sustainability of the system. Based on the set of interviews with a sample of socio-economic system representatives, stereotypes are captured and modelled with the help of causal loop diagrams. After several modelling iterations that synchronised the acquired models with the obtained responses, four main key stereotypes were identified-quality, ego, competence, and motivation. Both dominant feedback loops and important multi-input and multi-output variables are used for their description. Thus, the models provide an endogenous explanation of their importance for sustainability and help to identify its key factors.