How to improve individual learning effectiveness has always been an important research question. In practice, there is an interesting phenomenon of knowledge fortuitous re-encountering, which most people experience occasionally. However, there is no theoretical research in this field. Based on empirical observations, it has been found that people may re-encounter the same or similar knowledge by chance in different situations. This knowledge is presented in various rich forms, which will bring about affective and cognitive changes, ultimately influencing the learning effect. This concept, knowledge fortuitous re-encountering, is proposed as an important supplement to systematic, rational, and predictable individual learning. Its influence on learning is then introduced and systematically expounded upon from the perspectives of affection and cognition. In terms of affection, knowledge fortuitous re-encountering is believed to help strengthen individual affective perception, including general and specific perceptions. Specifically, knowledge fortuitous re-encountering helps individuals to recognize the importance of knowledge and the sense of “Yuan Fen” of knowledge. In the aspect of cognition, the characteristics of knowledge are first classified based on time-space theory. Furthermore, it is pointed out that knowledge fortuitous re-encountering is conducive to strengthening individual cognitive inspiration, encompassing divergent heuristics and convergent heuristics. Specifically, knowledge fortuitous re-encountering contributes to individuals’ cognition of the richness and unity of knowledge. Paying attention to knowledge fortuitous re-encountering and creating favorable conditions to create potential opportunities are important methods and keys to improving learning effectiveness. Furthermore, practical implications for creating potential opportunities for fortuitous re-encountering are put forward from the perspectives of internal and external causes. The theoretical development of related fields is advanced from three aspects. First, the concept of knowledge fortuitous re-encountering is clarified, emphasizing both fortuitous happenstance and differential re-encountering, aspects which has not been addressed in existing studies. Second, the influence mechanism of knowledge fortuitous re-encountering on learning is put forward. Specifically, it systematically analyzes this influence mechanism from the perspectives of affection and cognition, thereby advancing research in related fields. Third, the study of knowledge fortuitous re-encountering contributes to providing a new research perspective for individuals, teams, and organizations on how to improve learning effectiveness. In summary, the theoretical and practical discussion of learning from knowledge fortuitous re-encountering in this study aims to provide new ideas for improving learning effectiveness and inspire detailed exploration of individual learning research.