Further discussions:
Ayn Rand, "The Objectivist Ethics," in The Virtue of Selfishness: A New Concept of Egoism (New York: The New American Library, 1964), p. 21.

Leonard Peikoff, Objectivism: The Philosophy of Ayn Rand (New York: Dutton, 1991), pp. 251-259.

Tara Smith, Ayn Rand's Normative Ethics: The Virtuous Egoist (Cambridge: Cambridge University Press, 2006), pp. 106-134.