In line with the concept of 'nudging' people to change their behaviour, there has been increased attention on habit as a focus for psychologically-based health interventions. It is hoped that behaviours initiated by interventions not only become so regular that they are normalised into people's everyday lives, but that through repetition they may eventually become fixed and habitual. In this paper we draw on people's accounts of participating in a trial designed to encourage greater physical activity, and attend to the ways they describe their engagement with interventions within wider narratives of their everyday lives. In contrast to the idea that habit refers to automatic behaviour cued by external stimuli and governed by unconscious cognitive processes, our study describes how people identify many diverse elements that are felt to have equal significance in achieving a routine. Paradoxically, the sense of stability derives not from exact repetition, but from the ability for an assemblage of elements to be configured slightly differently each time. We consequently argue that attending to the diverse range of contextual elements bracketed off from interventions designed to be tested in trials, and the idea that continuity might emerge from variation, demands a reconceptualisation of the concept of habit adopted within many areas of current health psychology.