In reality and in the Objectivist ethics, there is no such thing as “duty.” There is only choice and the full, clear recognition of a principle obscured by the notion of “duty”: the Law of Causality.
The proper approach to ethics, the start from a metaphysically clean slate, untainted by any touch of Kantianism, can best be illustrated by the following story. In answer to a man who was telling her that she’s got to do something or other, a wise old Negro woman said: “Mister, there’s nothing I’ve got to do except die.”
Life or death is man’s only fundamental alternative. To live is his basic act of choice. If he chooses to live, a rational ethics will tell him what principles of action are required to implement his choice. If he does not choose to live, nature will take its course.
Reality confronts man with a great many “musts,” but all of them are conditional; the formula of realistic necessity is: “You must, if—” and the “if” stands for man’s choice: “—if you want to achieve a certain goal.” You must eat, if you want to survive. You must work, if you want to eat. You must think, if you want to work. You must look at reality, if you want to think—if you want to know what to do—if you want to know what goals to choose—if you want to know how to achieve them.
In order to make the choices required to achieve his goals, a man needs the constant, automatized awareness of the principle which the anti-concept “duty” has all but obliterated in his mind: the principle of causality—specifically, of Aristotelian final causation (which, in fact, applies only to a conscious being), i.e., the process by which an end determines the means, i.e., the process of choosing a goal and taking the actions necessary to achieve it.
In a rational ethics, it is causality—not “duty”—that serves as the guiding principle in considering, evaluating and choosing one’s actions, particularly those necessary to achieve a long-range goal. Following this principle, a man does not act without knowing the purpose of his action. In choosing a goal, he considers the means required to achieve it, he weighs the value of the goal against the difficulties of the means and against the full, hierarchical context of all his other values and goals. He does not demand the impossible of himself, and he does not decide too easily which things are impossible. He never drops the context of the knowledge available to him, and never evades reality, realizing fully that his goal will not be granted to him by any power other than his own action, and, should he evade, it is not some Kantian authority that he would be cheating, but himself . . . .
A disciple of causation is profoundly dedicated to his values, knowing that he is able to achieve them. He is incapable of desiring contradictions, of relying on a “somehow,” of rebelling against reality. He knows that in all such cases, it is not some Kantian authority that he would be defying and injuring, but himself—and that the penalty would be not some mystic brand of “immorality,” but the frustration of his own desires and the destruction of his values . . . .
Accepting no mystic “duties” or unchosen obligations, he is the man who honors scrupulously the obligations which he chooses. The obligation to keep one’s promises is one of the most important elements in proper human relationships, the element that leads to mutual confidence and makes cooperation possible among men . . . .
The acceptance of full responsibility for one’s own choices and actions (and their consequences) is such a demanding moral discipline that many men seek to escape it by surrendering to what they believe is the easy, automatic, unthinking safety of a morality of “duty.” They learn better, often when it is too late.
The disciple of causation faces life without inexplicable chains, unchosen burdens, impossible demands or supernatural threats. His metaphysical attitude and guiding moral principle can best be summed up by an old Spanish proverb: “God said: ‘Take what you want and pay for it.’” But to know one’s own desires, their meaning and their costs requires the highest human virtue: rationality.
— Ayn Rand from the essay, “Causality Versus Duty” in her book Philosophy: Who Needs It. Details here.