If a man says to himself that he must get a job for the sake of sustenance, then he has discovered a certain necessity from an end. But if that man happens to be a father, then the sustenance with which he is concerned is not merely his own; it is also the sustenance of his family. For this reason, the necessity seems stronger. If he is concerned only with his own sustenance, then it seems that he has something of a freedom to "opt out" of the end, or at least to pursue it with less priority.
In a similar manner, society and the political authority behind it concern some shared good. Indeed, the notion of a shared good is the very basis of authority; some individuals are given authority over others only because several individuals are working toward a shared good,