Why do the two self-regulatory modes of locomotion and assessment show opposite associations with mental health & well-being? To address this question, we examined whether social capital explains these links and whether regulatory modes and personality traits differentially predict mental health & well-being. Using data from the Young Adult Survey Switzerland (YASS; weighted N = 4,981), we tested mediation and moderation models including locomotion, assessment, extraversion, and neuroticism. Results showed that social capital partially explained why assessment was negatively and locomotion positively related to mental health & well-being, and that personality traits were overall stronger predictors than regulatory modes. Moreover, locomotion buffered the negative associations of assessment and neuroticism with social capital, though not with mental health & well-being itself. These findings advance our understanding of how dispositional and self-regulatory factors jointly shape social connectedness and mental health & well-being, and suggest that interventions fostering locomotion while sensitively addressing assessment tendencies may strengthen both social resources and mental health.