In democratic politics the public good is the same sort of concept. It, too must be discovered. Often the public goods is considered to be some specific state of affairs or hierarchy of ends which “the people” are supposed to favor. This misconstrues its nature. Beyond the most general formulations, there is substantial disagreement as to what measures are or are not in the public good. Given the enormous complexity of contemporary political issues, any reasonable person would admit to considerable uncertainty as to what specific programs will be most in keeping with the public good. This has lead some political scientists to deny that the concept carries any theoretical or practical weight at all.
Gus DiZerega (1994), Federalism, self-organization and the dissolution of the state
And that is why you should not believe a word any politician says when they start appealing to notions of the ‘public good’. It doesn’t exist. And even if it did, it is entirely disingenuous to suggest you have a clue as to what it might be. See also Hayek on dispersed information, and Shackle and Lachmann on radical subjectivity and kaleidics.