Life, according to philosopher Ayn Rand, is “a process of self-sustaining and self-generated action.”
Morality is the “science of self-preservation” and human fulfillment.
Self-interest indicates the end (the self) of one’s actions; rational indicates the means (reason) of obtaining that end.
Virtues are the mental and physical actions necessary to obtain the values necessary to sustain one’s life and achieve happiness.
If one desires consistent results, one must act consistently. That is, on principle.
Rational self-interest does not mean sacrificing oneself for others (what philosopher Auguste Comte coined as altruism or “otherism”) or sacrificing others for oneself (what is smeared as “selfishness”).
Rational self-interest means to live by the trader principle.
Ethics is individual morality applied to living life in society.