During the last decade, the Behavioural Insights Team (BIT) has been the main driver of establishing behavioural public policy as a novel approach in public policy. Adhering to a set of strategic principles, BIT has succeeded in translating insights from the behavioural science literature into policy interventions to show how behavioural science may be applied to public policy in a methodologically as well as economically efficient way. However, as Sanders, Snijders and Hallsworth (2018) note in their paper, the wide-ranging transformation of public policy development that many thought possible has remained absent. In this comment, I argue that this situation itself is due, at least partly, to the strategic principles adopted by BIT, and I call for developing more ‘diagnostic’ approaches, including better tools and models, to ensure that behavioural science is not perceived as offering merely technocratic tweaks.