The book that Robbie tries to lend to Baby as an explanation for his refusal to help Penny is "The Fountainhead" by Ayn Rand. Rand was the creator of a philosophy called Objectivism, which holds (amongst other beliefs) that it is more important for a person to be concerned with his or her own well-being rather than to try to help others. Some of her adherents (including, apparently, Robbie) interpret her books as justification for selfish and self-serving behavior, and the disavowal of responsibility to others.