論文アブストラクト：Strong user engagement with digital technologies for behaviour change is often taken as a precursor to their longer-term efficacy. We critically examine this assumption through a qualitative study of a smoking cessation app, called NewLeaf, which allows quitters to swap personal stories. The study examined what influenced people to engage or disengage with NewLeaf, and how the app was deployed in quit attempts during a four week trial. Several properties of swapped stories were reported to promote engagement, including: authenticity, currency, contextualization of advice, and evoking a sense of community. But while the resulting engagement was sometimes productive in supporting quitting, other trajectories of use were observed involving counterproductive engagement, and a surprising pattern of productive disengagement especially among stronger quitters. We discuss how this analysis of different trajectories problematizes any simple interpretation of user engagement as an early indicator of success for behaviour change technologies.