This Chapter is a dialogue from the Yellow Emperor's Classic of Internal Medicine, exploring the etiology of disease within a framework of cosmic forces. Qi interaction (Qi Jiao), the interplay of ascending and descending energies, is identified as central to health and disease. Imbalances in Qi Jiao, caused by encounters and suppressions of elemental energies, result in various illnesses. The text details specific years and their associated imbalances, linking them to disease manifestations and suggesting treatments. Finally, it discusses the role of "losing guard," a state where the spirit loses its proper position, resulting in vulnerability to evil spirits and death.