Aside from all the great comments here already, I've also seen it put like this:
Communism is a social-economic-political system designed to put people first and improve everyone's life. This is (after the revolution at least) a systemic and structural thing, not a choice of individuals. You can be awful and selfish, but you'll either be punished for it or it will end up helping society anyway.
By the same logic, someone who genuinely wants working people's lives to improve under capitalism isn't going to get anywhere. The entire system stands against pro-social choices.
Those are the negative feedbacks, the positive ones are that the people who uplift others will themselves be uplifted in a communist society. In capitalist societies those who are the most selfish and sociopathic are successful by the definition of the system and are promoted by it.