As people gradually age, they become prone to various ailments; old things become riddled with problems, making it difficult to reverse the accumulated issues.

The term "illness" literally refers to the occurrence of unhealthy phenomena in living organisms, encompassing defects, errors, damage, harm, dissatisfaction, blame, and so on. Some predictive texts suggest that "illness" implies meanings such as disease, lesions, plague, annoyance, hatred, enemies, hostility, shortcomings, defects, deficiencies, faults, weaknesses, loopholes, pain points, critical points, mental afflictions, corruption, and problems.

Generally speaking, a Ba Zi (八字) chart with "illness" indicates a person who acts slowly and overthinks. Those who sit in the position of illness are particularly sensitive and may miss opportunities due to excessive consideration. Such individuals are fond of public welfare, often eager to contribute their utmost, and exhibit extreme love and hate, with a penchant for cleanliness and a resolute character, yet possessing good manners. Although somewhat sensitive, they do not regret their actions. People with a Yin (阴) day master have an unstable and somewhat withdrawn personality, and they may struggle to get along harmoniously with their siblings.