Social comparison is a vague concept that is controversial from its basic definition to its further application as the original language from Festinger 1954 is too vague and unscientific. There are few articles responsible for clarifying the basic role of social comparison. Therefore, this article aims to clarify the effects and reasons for social comparison on the base of a socially acceptable definition of social comparison. The article will review several scientific research in specific aspects, and then try to string them together and form a general solution. The study demonstrates that the desire for self-realization or self-improvement will motivate social comparison, and these two motivations will function differently according to different directions of social comparison. In addition, motivations will contribute to the various effects of social comparison, and there is a negative correlation between social comparison orientation or upward social comparison and self-realization in the SNSs field. Both systematical reviewing and further suggestions are discussed in this article.