The notion of forgetting implies that important information once learned and accessible can no longer be retrieved and remembered. Although college students do not need to recall everything, they frequently have some trouble remembering what they need to know when taking quizzes and examinations (exams), and when giving oral presentations. This article offers six major explanations why college students tend to forget some of the course materials they learned from instructors' perspectives. These six explanations include decay, interference, failure to store or consolidate, failure to retrieve, reconstruction error, and obliterative subsumption. For each explanation of forgetting, college instructors must utilize certain instructional strategies that would minimize forgetting important course information taught in class in order to facilitate students learning and promote long-term retention of course materials.