Heaven is eternal and earth is everlasting. The reason why heaven and earth are eternal is because they do not live for or by themselves: that is the reason they ever endure.
The perfect Sage, who puts his own interests behind him, is always the leader of his people. All the time he is looking after the welfare of his people and in doing so he preserves his own life. Is it not because he is disinterested that his own interests are conserved?