Appeals to authority, of varying types, are a major tool of persuasive essays. By appealing to some sort of authoritative power, the essay writer tries to convince the reader that their stated position is correct. In the essay "Corn-pone Opinions," Mark Twain makes several appeals to convince the reader; one of these is the "Appeal to Common Sense." Mark Twain considered his readership to be of typical intelligence, the type who understand common sense positions on things like conformity:

Was the resentment reasoned out? Was the acceptance reasoned out? No. The instinct that moves to conformity did the work. It is our nature to conform; it is a force which not many can successfully resist. What is its seat? The inborn requirement of self-approval. We all have to bow to that; there are no exceptions.
(Twain, "Corn-pone Opinions," paulgraham.com)

Most people want to gain the approval of other people, and better yet, of an entire society. To go along with fashion trends is to be instinctively approved-of by others; to go against fashion is to be instinctively disapproved-of. By appealing to common sense, Twain leaves the reader with the feeling that "everyone knows this, therefore my conclusion should be correct; it's just common sense!" This bolsters Twain's position that no "opinion" is truly objective, but instead all opinions come from both overall societal opinion, and from subjective experience.