This chapter explores zemblanity as the logical inverse of serendipity: not the happy realization of unintended benefits, but the gradual, self-generated emergence of foreseeable harm. Moving from the story of Barbara Hutton to everyday cognitive habits, it traces how individuals can drift into misfortune through premature coherence, interpretive narrowing, and the erosion of slack in probabilistic environments. It then broadens the lens to show how minimal acts of agency position people and organizations within different fields of possibility, where exposure rather than outcomes is chosen, and where the curvature of those fields (concave or convex) shapes the likelihood of either serendipity or zemblanity. At the organizational level, the chapter situates zemblanity within the dark side of learning, showing how experience, correction, capability, and coherence can invert and quietly entrench maladaptive trajectories. Finally, it extends the concept to large sociotechnical systems, using illustrative cases to show how ordinary decisions, taken over time, can assemble structural fragilities that later manifest as “sudden” catastrophe. Across these levels, zemblanity is presented as an emergent pattern of endogenous decline, authored through repetition, attachment, and the failure to revise course even when warning signs are abundant.