Quality defects tend to be tenacious. Often they linger at a certain level, even after the most sophisticated quality management techniques have been deployed. This is usually because the root causes have not been accurately diagnosed. This book chronicles a series of eight dramatized, real-life cases, through the medium of a professor-protegee relationship, leading to a formal technique called Differential Diagnosis. This technique is unique, because it is based on "backward thinking", while most other techniques use "forward thinking". The real-life cases demonstrate how to overcome the difficulties of application, allowing the practitioner to transcend from knowledge to profound knowledge.