The challenge of manners is not so much to be nice to someone whose favor and/or person you covet (although more people need to be reminded of that necessity than one would suppose) as to be exposed to the bad manners of others without imitating them.

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

“Miss Manners,” syndicated column (1987-11-01)
    (Source)

Collected in Miss Manners' Guide for the Turn-of-the-Millennium, Part 1 "Revised Conventions," "Correcting Others" (1989).