I have been thinking a lot recently about self-interest. In a workshop I give on leadership I begin by describing life as a conflict between self-interest and morality. When you take responsibility for other people that dichotomy expands to include a third part " mission", which leads to the concept of leadership.
In an HBS research paper "Naivete and Cynicism in Negotiations and Other Competitive Contexts" the authors discuss the role of self-interest in negotiation in terms of naivete and cynicism. Their concepts are captured in the summary below.