This chapter introduces and theorizes zemblanity as a condition of organizational decline characterized by the unintended realization of foreseeable harm. The chapter defines zemblanity as a cumulative and internally generated phenomenon, unfolding through three necessary conditions: agency, recurrent engagement with errors, and the endogenous construction of misfortune. Traced across illustrative cases, these mechanisms reveal that organizational misfortune is often structurally embedded and behaviorally maintained rather than externally imposed. Building on this theoretical grounding, the chapter advances a systemic model identifying deteriorative culture, leadership deficiencies, and structural inefficiencies as the root causes of organizational zemblanity. Strategic agility is presented as the structural counterpoint to this condition, illustrated through a case in which a major firm in the mobile phone industry successfully deployed agility to avert a zemblan decline. The chapter then introduces a structured diagnostic framework for assessing the conditions under which organizations are likely to experience zemblanity. Drawing on a tripartite lens encompassing structure, culture, and leadership, it presents the Zemblan Score (ZS), a self-assessment instrument designed to detect early-stage organizational vulnerabilities. The approach disaggregates each root cause into subcomponents and operationalizes them through 12 Likert-scaled items.