When Siblings Cannot Mourn Together: A Developmental Theory of Rivalry, Polarization, and Estrangement
Abstract
Sibling rivalry and adult estrangement are common relational outcomes, yet existing explanations rely heavily on attachment style divergence, parental favoritism, or discrete traumatic events. These approaches describe relational patterns but offer a limited account of why sibling polarization persists despite insight, goodwill, or therapeutic intervention. This article addresses this gap by proposing a developmental theory in which sibling conflict and estrangement emerge from a structurally ungrieved family loss rather than from competition or personality differences. Drawing on a stage-based model of emotional development, the paper introduces the concept of fear–anger collusion, in which Stage-1 fear and Stage-2 anger function as complementary regulators that stabilize the family system by preventing grief. Within this configuration, siblings differentiate into divided survival identities—one organized around attachment vigilance, the other around control and emotional detachment—thereby distributing unprocessed grief across relational roles. The article further examines how adult attachment dyads often reinforce this arrest, rendering sibling reunification developmentally destabilizing. The proposed framework reframes sibling rivalry and estrangement as outcomes of arrested mourning rather than relational failure, with important implications for developmental theory, clinical ethics, and the limits of reconciliation-focused interventions.