Psychological suggestion was a psychological phenomenon that referred to the corresponding changes in one's psychology and behavior under the influence of a certain belief, attitude, or concept. It could be positive or negative. In some cases, psychological suggestion may be considered a manifestation of mental illness. However, it is important to note that psychological suggestions are not always related to mental illness. They can be the result of other psychological phenomena. Therefore, the evaluation of psychological suggestion needed to be analyzed according to the specific situation.