The document discusses the Theory of Unpleasant Symptoms, which is a nursing theory used to evaluate patients' symptoms. The theory focuses on three key elements: the symptoms themselves, factors that influence the symptoms, and how the symptoms impact the patient. Nurses use assessment tools informed by this theory to comprehensively examine a patient's symptoms by considering physiological, developmental, social, and other relevant factors. Properly applying the theory helps nurses select the most appropriate assessment method and treatment approach for each patient.