Unlocking the power of the family: emotional resilience as the critical threshold for the protective role of family functioning against adolescent Internet addiction

Abstract Objective Although both family functioning and emotional resilience are recognized as protective factors for adolescent Internet addiction, the precise synergistic mechanism linking them remains unclear. In particular, it is unknown whether an individual’s level of emotional resilience serves as a prerequisite for the family environment to exert its protective effect. Methods This study employed a two-year longitudinal design, following 7,853 junior high school students across two assessment waves. Multilevel linear models with cluster-robust standard errors were used to test main effects and the interaction between family functioning and emotional resilience, while lagged models examined causal directionality. The Johnson‑Neyman technique was applied to probe the moderation pattern of emotional resilience. Results Longitudinal analyses confirmed that both family functioning (β = -0.168, 95% CI: -0.212~-0.124, p < 0.001) and emotional resilience (β = -0.137, 95% CI: -0.165~-0.109, p < 0.001) are significant independent protective factors against Internet addiction. Interaction analysis, however, revealed a finding: emotional resilience and family functioning interact negatively (β = -0.0065, 95% CI: -0.0091~-0.0039, p < 0.001). Johnson‑Neyman interval analysis identified a clear emotional-resilience threshold (score = 21; observed range = 11–66). Only when an individual’s emotional-resilience level exceeds this critical point does high family functioning significantly reduce the risk of Internet addiction; for adolescents whose emotional-resilience scores fall below the threshold, the protective effect of the family environment disappears. Conclusion This study moves beyond the simple confirmation of independent protective factors and proposes a ‘protective-factor activation threshold model’ — an emotional resilience ‘switch’ that must be tripped before family support can protect against addiction. The findings indicate that emotional resilience is not merely a co-protective factor with family functioning but functions as a psychological “switch” that activates the family’s protective influence. This has clinical implications: for youths with low emotional resilience (≤ 21), interventions targeting the family environment alone are likely to fail. Effective prevention strategies therefore must be dual-focused, simultaneously and preferentially enhancing individual emotional resilience levels to “unlock” the potential of the family support system.