The paper describes a partnership project between three parties, centred on the use of System Dynamics (SD) in a Mental Health Trust (MHT). The main learning experiences relate to the politics of introducing challenging concepts in a situation where participants prefer to avoid confrontation. The rigorous nature of SD modeling and simulation raises questions which operational managers may fear reflect badly on the organization and their own capabilities. They may be uncomfortable with questions about the evidence-base for current treatments, or the research to back their ideas for future developments. A further issue is the ambiguity inherent in definitions of SD and the likelihood that many managers prefer single-issue projects, based on their comfort zone of practice/expertise. A hypothesis is developed to describe the observed reactions in the project and suggest alternative approaches in carrying out SD projects in the UK public sector.