The true self is not a self alone. Giving life to the self requires that one give life to the surroundings of the self; the self must harmonize with the surroundings.
If you live by the principle "If it's good for me, then it's good." And give no thought to others, you will induce others to dislike and go against you, and ultimately you will fall into isolation and despair.
This also holds for business. A shopkeeper who sells shoddy merchandise for high prices and pursues gain only for himself will in time lose customers and decline. But businesses that neglect profit will likewise not last long. The important thing is that because a business and its customers are inseparable and mutually dependent, they coexist and co-prosper by always finding how they can realize mutual gains.
Likewise with human beings: if the two sexes were to continually reject each other and live in disharmony, humanity would disappear from the Earth inside a century. When men and women live in harmony by making the best of each other's strong points and complement each other's weak points, they create harmonious homes, have children, and thereby perpetuate their stock.
However, people are wont to run counter to this law of nature, ignore others, and seek benefit for their own selves only. But although they may realize gain temporarily, the net result will be eventual isolation and ruin.
On the other hand, from long ago there is the term "misplaced benevolence"* meaning that it is also a mistake to have futile compassion or ill-timed pity for someone and be biased toward the other party's benefit. This is called altruism, and it will lead to one's own ruination just as surely as the egoism discussed above. Thus in any human endeavor, people will be able to co-exist and co-prosper, and to realize perpetual advancement by steering the middle ground between egoism and altruism, and continually looking for the midpoint where the interests of both oneself and others coincide.
Such an arrangement is called the unity of self and other, and it accords with the law of nature.

(* This term literally means "the benevolence of Duke Xiang of Song." The term is based on a story from Chinese history, in the era from 772 B.C. to 381 B.C. The story is about Duke Xiang from the Song region. When about to do battle with an army from the Chu region, the Duke followed his idea of how a man of virtue should behave, and delayed his attack until the Chu army had readied its battle formation. As a result of this delay, the Chu army defeated the Duke's army.)