Intro: When confronted with major threats such as the COVID-19 pandemic, people often experience (temporary) decline in well-being. The central purpose of this study was to identify mechanisms underlying stability and change of well-being in times of threat like the COVID-19 pandemic. We examined change in mental health symptoms and its relationships with appraisals of the pandemic and daily life experiences during the pandemic, including affective states, stress, and mindfulness. Methods: We conducted a study across 3.5 weeks, including pretest, posttest, and a diary phase in-between. In this report, we worked with a sample of 460 adults, pre- and post-test information, as well as a total of 7189 observations from the diary phase. Results: Results showed that less fortunate change in mental health symptoms across three weeks was predicted by more negative affect and less mindfulness, specifically less attention to the present moment, in daily life. Furthermore, less fortunate change in mental health symptoms was correlated with change towards less fortunate appraisals of the appraisals. Finally, we showed that more general views of the pandemic (i.e., appraisals) were interrelated to experiences in daily life, with more negative appraisals of the pandemic predicting more negative affect and stressor occurrence as well as less mindfulness.Discussion: These findings speak to the dynamic nature of well-being and appraisals in times of threat, and they show how experiences in daily life matter for change in well-being