Self-efficacy predicts differential neuroticism change in a smartphone-based intervention.

Self-guided, digital interventions can help people change their personality traits in desired directions, including becoming less neurotic. However, little is known about how and why people differ in intervention-related changes. Theoretical models state that intentional personality change must be perceived as feasible and that being motivated to change is not sufficient to elicit lasting trait changes. Using a German-speaking sample (N = 446; Mage = 25.88; 85% female; Residence: 47% Switzerland, 26% Germany, 26% Austria, 1% other), we tested whether self-efficacy and growth mindset predict change in multiple neuroticism measures across a 6-week intervention and 2-month follow-up. To isolate temporal processes during the intervention, we examined codevelopment of weekly neuroticism and self-efficacy and their week-to-week temporal associations. We found evidence for self-efficacy predicting differential neuroticism change but not for growth mindset. Participants with higher self-efficacy showed greater pre-post decreases in self-reported neuroticism and greater pre-post increases in emotional resilience than those with lower self-efficacy. At follow-up, participants with higher self-efficacy continued to improve more in neuroticism and emotional resilience. Last, higher self-efficacy in 1 week predicted lower neuroticism in the following week, and vice versa, independent of participants' overall trajectories. In contrast, there was no consistent evidence for between-person codevelopment of weekly self-efficacy and neuroticism across the intervention. Findings support theoretical expectations that perceived feasibility is a precondition for neuroticism change and suggest possible reinforcement mechanisms between weekly self-efficacy and neuroticism. We discuss implications for theory and future intervention studies. (PsycInfo Database Record (c) 2026 APA, all rights reserved).