Etiquette is about all of human social behavior. Behavior is regulated by law when etiquette breaks down or when the stakes are high — violations of life, limb, property, and so on. Barring that, etiquette is a little social contract we make that we well restrain some of our more provocative impulses in return for living more or less harmoniously in a community.

Judith Martin (b. 1938) American author, journalist, etiquette expert [a.k.a. Miss Manners]

“Polite Company,” interview by Hara Estroff Marano, Psychology Today (1998-03)
    (Source)