Self-Regarding Good, Public-Regarding Good, and Shared Happiness: Mechanisms of Compatibility Between Individual and Common Interests—A Relational Theory from Zero-Sum Conflict to Mutual Gain

The relationship between individual interest and the common interest is a persistent problem in ethics, economics, political philosophy, and social theory. Many social conflicts can be understood as competition among interests, yet actual human cooperation repeatedly demonstrates that self-interest and other-regarding concern are not always locked in a zero-sum opposition. Market exchange, knowledge creation, care, education, public service, and long-term reciprocal relationships can all improve the condition of the actor while also improving the conditions under which others live. The relevant question is therefore not simply whether individuals should be selfish or altruistic, but how individual interests are realized, under what conditions those modes of realization are compatible with the interests of others, and when compatibility can develop from non-harm into mutual gain. Building on Paper 01 (Hua, 2026d), the Dynamic Coordination Theory of Happiness (DCTH), and Paper 02 (Hua, 2026e), the Relational Embeddedness and Social Transmission Model, this paper develops the mechanism of the public-regarding realization of self-regarding good. "Self-regarding good" refers to self-directed value claims through which an agent seeks to maintain, improve, and develop a legitimate state of life; it is not equivalent to selfishness in the pejorative moral sense. "Public-regarding good" is not the economic concept of a public good. It refers instead to other-regarding value creation through which an agent, by means of products, services, knowledge, care, cooperation, rule-following, or other action, improves the legitimate conditions of others, society, future generations, or the natural environment. The central argument is that individuals need not improve their own well-being by depressing the well-being of others. They can realize legitimate self-regarding goods by creating value that improves the legitimate self-regarding goods of others, while receiving returns through exchange, reciprocity, trust, reputation, meaning, social recognition, and institutional incentives. Self-regarding good and public-regarding good are therefore not two absolutely opposed moral poles. They can form a circular structure: self-regarding good supplies motivation for action, public-regarding good creates relational value, and reciprocity and institutions connect the two into sustainable cooperation. This transition is not automatic. Public-regarding action must satisfy five conditions: the underlying need must be basically legitimate; the autonomy of others should be respected; the contribution should match real needs; the burden should not be imposed indefinitely on a single actor; and short-term satisfaction should not be purchased through greater long-term harm. The paper accordingly distinguishes five modes of realizing self-regarding good: predatory, exclusionary, compatible, reciprocal, and generative. It then develops eight theoretical propositions and an empirical research agenda. The core claim is not that individual interest should be abolished, but that its realization structure can be transformed. Shared happiness does not require people to stop living for themselves. It requires expanding the range of ways in which people can realize themselves through actions that also create value for others, society, and the future.