question regarding selfishness and altruism
Why is it possible to live for the self rationally, as a primary motive, and without sacrifices, but not possible to live for others rationally, as a primary motive, and without sacrifices? In other words why is 'rational other-interest' logically impossible but it suddenly becomes all-possible when the self is the beneficiary?
You’re basically just asking for justification of the objectivist ethics here. You should check out Objectivism: The Philosophy of Ayn Rand or The Virtue of Selfishness.
Because if everyone lived for others no one would live at all.