Quotes Uncovered: Trying Again and Fooling People

Each week, I’ve been inviting readers to submit quotations for which they want me to try to trace the origin, using The Yale Book of Quotations and my own research. Here is the latest round:
Science Frustrated asked:
“So who said, ‘once you don’t first succeed, try try again?'”
The Yale Book of Quotations, which attempts to trace all famous quotations to their earliest findable occurrence, traces “If at first you don’t succeed, try, try, try again” to a poem titled “Perseverance; or, Try Again,” printed in Common School Assistant, Aug. 1838. No author is identified.
Mary Kathleen Kisiel asked:
“One of the history textbooks from my childhood attributed this to P.T. Barnum: ‘You can fool all of the people some of the time, and some of the people all the time, but you can’t fool all of the people all of the time.’ I think it has a plausible completeness, don’t you?”
This is usually attributed to Abraham Lincoln. The YBQ traces the Lincoln attribution as far back as the New York Times, Aug. 27, 1887, and notes: “According to The Collected Works of Abraham Lincoln, ed. Roy P. Balser, ‘Tradition has come to attribute to the Clinton [Illinois] speeches [September 2, 1858] this ‘most famous’ of Lincoln’s utterances. Basler indicates, however, that there is no evidence of this saying in Lincoln documents. P. T. Barnum has also been a putative source for the quotation.”
Ann asked:
“Where does the admonition ‘Don’t kill the messenger!’ originate? Some say it has something to do with the story of Marathon.”
The earliest version traced by the Yale Book of Quotations is “Nobody likes the man who brings bad news,” from Sophocles‘ 5th century B.C. play, Antigone.
Ceolaf asked:
“Here’s a recent one, I think. ‘I for one welcome our new [something] overlords.’ Language log says that Kent Brockman first uttered this when he said, ‘And I for one welcome our new insect overlords,’ on February 24, 1994. Is he really the source?”
Yes.
Do any readers have any other quotations whose origins they would like me to attempt to trace?