Preventive health actions are often explained as consequences of individual knowledge, motivation, risk perception, or willingness. Such explanations are incomplete when the same person may act differently across diseases, social settings, institutional environments, and moments of changing uncertainty. This article develops a behavioral ecology account of prevention in which health action emerges from the interaction of perceived threat, collective meaning, social-network exposure, institutional trust, practical opportunity, and expectations about other people’s behavior. The framework distinguishes psychological appraisal from observed behavior, interpersonal influence from institutional conditions, and willingness from the capacity to act. Culture is treated not as a fixed group attribute but as a context shaping norms, legitimacy, and social consequences. Social networks are represented as channels through which information, expectations, and behavior can diffuse without assuming that observed similarity proves contagion. Trust is disaggregated by institutional object and linked to both credibility judgments and prior institutional experience. Material costs, accessibility, and service organization define unequal opportunity structures within which intentions become more or less actionable. The article proposes that prevention is best understood as context-dependent coordination under unequal constraints. This model generates bounded predictions for intervention design and public communication while requiring empirical validation across populations, behaviors, institutions, and time.
