One of the guiding principles is to "dispel evil and support the good." In addition to treating illness, TCM focuses on strengthening the body's defenses and enhancing its capacity for healing and to maintain health. TCM encompasses how the human body interacts with all aspects of life and the environment, including the seasons, weather, time of day, our diet and emotional states. It sees the key to health as the harmonious and balanced functioning of body, mind and spirit, and holds that the balance of health depends on the unobstructed flow of qi (pronounced chee) or "life energy" through the body, along pathways known as meridians. TCM practitioners see disease as the result of disruptions in the circulation of qi. TCM can be particularly effective for complex diseases with multiple causes, including metabolic diseases, chronic and degenerative conditions (such as knee arthritis) and age-related diseases.