Nudges have become a popular tool for behaviour change; but, some interventions fail to replicate, even when the identical, previously successful intervention is used. One cause of this problem is that people default to using some of or all of the previously-successful existing nudges for any problem—the “kitchen sink” approach. We argue that the success of an intervention depends on understanding people’s current behaviour and beliefs to ensure that any nudge will actually “budge” them from their current beliefs. We introduce (...) the Beliefs–Barriers–Context model, with three components: understanding beliefs, barriers, and context to change behaviour through a budge. Designing a budge has the goal of identifying the psychological mechanism that drives a target behaviour, focusing on the psychology of the target population before attempting to change that behaviour. In contrast to the “kitchen sink” approach, budges are best complemented with mechanism experiments to identify what undergirds behaviour change. Moving away from simply nudging behaviour to budging minds—by understanding beliefs, barriers and context—has the potential to inform both the successes and failures of behavioural interventions. (shrink)