Behavioural economics (BE) is the buzzword of the moment; in government, policy, finance and more recently, marketing. Marketers wonder if this is the latest fad, or if BE holds truly transformative potential. We believe that BE is not a fad and more than a tool. BE is a large body of knowledge, collected in lab and in field over several decades, removing the mystery around decision making. The key insight from BE is that humans do not make rational decision, but rationalize the decisions they make. Traditional market research practices rely on rationality, relegating insights to the post-rationalization process. In contrast, behavioural methods can access valid insights into the actual motivators of a decision. To highlight this, we will present a case study comparing insights from traditional market research to insights from a behavioural approach.