Because the essence of selfishness is self-interest, but selfishness to a certain extent will deviate from moral values, resulting in the inability to achieve self-interested goals, so for strict egoists, it is necessary to pursue the maximization of interests, they cannot tolerate being placed in a moral depression, and cannot accept any passive situation that may affect further profits in the future.
It is human instinct to seek advantages and avoid disadvantages, and every activity carried out by individuals is to seek benefits, and the group is composed of several individuals who have the same interests in a certain aspect. However, in group life, the factors that affect people are not only the same interests: we are brought together by the same interests, but we are not exactly the same individuals, and various factors in other aspects will affect the value judgment between individuals, and the value judgment will affect the degree of benefit of each individual. Selfishness is used to describe those who make a profit and even seek their own profit by infringing on the rights and interests of others.
For example, if we form a team because we recognize a project, the project is our unanimous interest. However, in addition to the benefits of the project, the perception of individuals is different, and some people will think that they should get more, but the total income of the project is fixed, so they can only use the way of infringing on the rights and interests of others to benefit. However, such behavior will be disgusting to the rest of the team, which in turn will affect the eligibility to participate in other projects in the future. Therefore, it is necessary to beautify the infringement to at least achieve procedural justice, and hating but not violating the law, legal but unreasonable are the common behavioral characteristics of these people. The rules of the group or the laws of the country often regulate the bottom line of people's behavior, and selfish people are often using the bottom line behavior to test the reaction of others and maximize their own interests.
Of course, profit is not limited to material benefits, but also includes emotional and emotional gains. As long as you are happy, you don't care if you hurt others, and after you are happy, you have to add a halo of "good for you" to yourself.
But selfishness to a certain extent will produce resistance, and when resistance becomes the common understanding of the group, even if you are the king of heaven, it is useless.