Does It Take Two to Benefit From Self‐Expansion? Dyadic Response Surface Analyses of Self‐Expansion and Relationship Satisfaction in Daily Life

Relational self‐expansion—the process of broadening one's self through novel and exciting experiences with a romantic partner—is important for relationship maintenance. Although theory and empirical research suggest that self‐expanding experiences enhance relationship satisfaction, it remains unclear whether partners need to experience similarly elevated levels of self‐expansion on a daily basis or similarly high levels of self‐expansion across time for these benefits to emerge. In four daily diary studies ( N = 512 couples), we assessed both partners' relational self‐expansion and relationship satisfaction across 21 consecutive days. Dyadic response surface analyses revealed no evidence that matching in daily fluctuations of self‐expansion or matching in heightened self‐expansion across time predicted greater relationship satisfaction. Instead, couples who reported higher self‐expansion reported higher satisfaction, and actor effects were consistently stronger than partner effects. Novel to this investigation, daily relationship satisfaction was lower only when self‐expansion was low, with moderate and high levels yielding similarly high satisfaction. These findings suggest that the overall level of self‐expansion of each partner's experiences, rather than similarity between partners, plays an essential role in sustaining relationship satisfaction.