In this paper, I propose that individualism and selfishness are embedded in every individual, and that their existence is needed to provide rationale for the actions of individuals. I argue that people are motivated by their targeted benefits as individuals, and rationalize their decisions to reach their individual targets using their selfishness in both individualists and collectivists cultures. As well, I propose that selfishness is good and is not a sin, and I introduce a new definition of selfishness. My approach and methodology in proposing my arguments depends on the conduct of thought experiments of the debated ideas, and on readers’ ability to undertake similar thought experiments and reach similar conclusions and understandings. I ask readers to conduct a mental experiment of the proposed ideas using the reasoning that I propose. I believe that thought experiments on individualism and selfishness and their role in the rationalization of human decisions could be easily conducted by all readers.