Why are ignorant people so confident? How do politicians utilize conflation to influence groups? Why do scientists fall for similar mistakes? How is complexity managed? Why does culture effortlessly shape what we can do? This book argues: Because of approximations! Incompleteness pervades our interactions with the world. Its effects on individual and group behaviors can foster creativity or create invisible prisons. We navigate incompleteness with approximations and, too often, end up on the 'dark side'. This book resembles a tourist's trip much more than a scientist's expedition, and is for anyone interested in a broader understanding of an individual's mental life and how identities, incompletenesses, and social contexts shape it. As we examine approximations and think about their origins and the problems they can create, the reader will encounter glimpses from physics, biology, philosophy of science, management, marketing, politics, systems theory, fuzzy logic, geometry, design and creativity, culture, and neuro-science and more... Fuzzy on the Dark Side is a book about incompleteness, creativity, thinking, identities, and systems. Roughly - it is an approximation of the 'Approximate Thinking' super idea.