Digital identity is an ongoing psychosocial process, not merely a representation of an offline person, through which individuals present, evaluate, and revise the self. This critical integrative review examines self-presentation, authenticity, social comparison, reflected appraisal, and online–offline self-discrepancy. It synthesizes peer-reviewed research published primarily between 2010 and July 2026 while retaining foundational theoretical works. Goffman’s dramaturgical model, Cooley’s looking-glass self, Higgins’s self-discrepancy theory, Foucault’s technologies of the self, Walther’s hyperpersonal model, and Turkle’s networked identity are integrated into a multilevel framework. The evidence indicates that social media effects depend on platform affordances, audience structure, user motives, developmental stage, and alignment between self-concept and expression. Authentic expression and supportive interaction may enhance well-being, whereas idealization, upward comparison, approval dependence, and persistent audience monitoring may contribute to psychological distress. The “black mirror” is developed as a non-fictional metaphor for the screen as stage, social mirror, archive, and algorithmic environment. Digital identity is therefore conceptualized as a negotiated relational system rather than a simple opposition between “real” and “virtual” selves. Future research should prioritize longitudinal, cross-cultural, platform-sensitive, and person-specific designs.