"The definition of insanity is doing the same thing over and over again and expecting a different result."

Source unclear but not Albert Einstein (a false quotation magnet on a par with Abraham Lincoln). Various diligent efforts have been made to determine its origin online (for instance here) but regardless of where it came from it has caught on because we humans make such diligent efforts to demonstrate its validity in real life.

"Include me out."

Sam Goldwyn, quoted in Gilbert! Magazine Vol. 4 #3 (December 2000)

"All human beings should try to learn before they die what they are running from, and to, and why."

James Thurber "American author (1894-1961)” quoted as "Thought du jour" in Globe and Mail May 30, 2013

"a mind, as H.G. Wells observed of the President [Franklin Roosevelt], 'appallingly open,' open indeed at both ends, through which all sorts of half-baked ideas flow…"

John T. Flynn, Country Squire in the White House, excerpted in S.I. Hayakawa Language in Thought and Action

"To the materialist things like nations, classes, civilizations must be more important than individuals, because the individuals live only seventy-odd years each and the group may last for centuries. But to the Christian, individuals are more important, for they live eternally; and races, civilizations and the like, are in comparison the creatures of a day."

C.S. Lewis “Man or Rabbit?” in The Grand Miracle

"The habit of contemplation, the ability to sit down in front of something and care enough to let it speak for itself, cannot be acquired soon enough."

Robert Farrar Capon, The Supper of the Lamb p. xiii.

"Think. Think hard."

G.K. Chesterton in Illustrated London News July 6, 1912 quoted in Gilbert Magazine Vol. 10 #3 (Dec. 2006)

"There is a saying; if you can’t dance, sit down."

Letter from "T.B. of St. Catharines" in NCC Freedom Watch Vol. 2 #13 (June 5, 2001)