Abstract
Self-trackers reflect on their personal data to understand their behaviour and plan accordingly. Often, this reflection involves uncertainty, which can affect decision-making. To better understand the role of uncertainty, we conducted an interview study to comprehend how uncertainty influences reflection and the resulting actions. Our findings suggest that, in addition to the conventional role of uncertainty as a barrier, uncertainty also manifests as a trigger and facilitator to reflection. We discuss functionalities to alleviate the negative effects of uncertainty (e.g. incorporating users' expectations in self-tracking), and leverage its positive effects through activity reconstruction mechanisms.