Whether a depressed person knows that he or she has depression is related to self-knowledge, which is also clinically called apprehension or introspection and refers to the patient’s ability to recognize and judge his or her own mental state. Self-knowledge is the ability to recognize abnormal mental activity and actively seek medical help for it. Lack of self-knowledge refers to the patient’s inability to recognize his or her own pathological manifestations, denying the existence of mental problems and believing that his or her mental symptoms are objective realities, and this type of patient often refuses to seek medical attention and treatment. In the case of depression, most patients have complete self-knowledge, they know they are sick, they are depressed, they can actively seek treatment, and they describe their condition and symptoms. However, there are some patients who know they are ill and become different from before, but do not know they have depression and believe it is due to external causes, such as environmental problems, work problems, and viral infections or the need for rest. This situation requires appropriate guidance for the patient so that he or she can be seen by the psychology department in a timely manner. In addition, patients with severe depression have incomplete self-knowledge or even no self-knowledge, in which case they often have obvious suicidal tendencies or are accompanied by psychotic symptoms. Patients lack a correct understanding of their current state and believe that they are redundant in the world and that death is the best relief, or they may fall into psychotic symptoms and repeatedly commit suicide or self-injury, or even abnormal behavior, despite the advice of relatives or doctors, or even lose the desire to seek treatment. In this case, family members should closely monitor the patient to prevent accidents and get the patient hospitalized as soon as possible.