nobody ever went broke underestimating the intelligence of the American people

Etymology
Widely attributed to American author and social critic (1880–1956) but not found verbatim in his published works, so the source and original form of this expression are not known with certainty. Likely a nearly verbatim paraphrase of: "No one in this world, so far as I know ... has ever lost money by underestimating the intelligence of the great masses of the plain people."

Proverb

 * 1) Americans, as a group, are not especially intelligent and can be readily entertained or fooled to produce a financial benefit for someone.
 * 2) * 1992 Feb. 14,, "Film: A Dim Duo In a Revel Of Stupidity" (review of Wayne's World), New York Times (retrieved 13 Sep 2015) :
 * H. L. Mencken may have noted that no one ever went broke underestimating the intelligence of the American people, but not even he could have anticipated this. Like Bill and Ted, their principal rivals among screen duos who play dumb, Wayne and Garth do their best to elevate stupidity to an art form.
 * H. L. Mencken may have noted that no one ever went broke underestimating the intelligence of the American people, but not even he could have anticipated this. Like Bill and Ted, their principal rivals among screen duos who play dumb, Wayne and Garth do their best to elevate stupidity to an art form.

Usage notes

 * In a common variant version of this proverb, the term is used instead of.