“It's a livin' thing.
It's a terrible thing to lose.
It's a given thing.
What a terrible thing to lose.”

"The Fact About Progress," The New York Times (1970-02-24)

Source: Where the Wild Things Are (1963); of this passage Bill Moyers stated in "NOW with Bill Moyers", PBS (12 March 2004) http://www.pbs.org/now/arts/sendak.html:
Context: And when he came to the place where the wild things are, they roared their terrible roars and gnashed their terrible teeth and rolled their terrible eyes and showed their terrible claws till Max said, "Be still" and tamed them with the magic trick of staring into all their yellow eyes without blinking once.
Context: And when he came to the place where the wild things are, they roared their terrible roars and gnashed their terrible teeth and rolled their terrible eyes and showed their terrible claws till Max said, "Be still" and tamed them with the magic trick of staring into all their yellow eyes without blinking once. And they were frightened and called him the most wild thing of all and made him king of all wild things.

Discussing rapidly-increasing education levels and competition from countries outside of the United States in a 2004 venture capital meeting in California, as quoted in "A Terrible Thing to Waste." https://www.nytimes.com/2009/08/02/magazine/02FOB-onlanguage-t.html The New York Times Magazine. July 31, 2009.
About the quote: Even though Romer made this statement approximately four years before the 2008 Financial Crisis and the subsequent Great Recession, policy makers repeated the idea frequently during the Crisis and the Recession as a reminder that necessary economic and financial reforms which were previously politically impossible were now quite feasible. (See, for example, "A Crisis Is a Terrible Thing to Waste," https://ssir.org/articles/entry/a_crisis_is_a_terrible_thing_to_waste Stanford Social Innovation Review, July 21, 2010).

Responding to an assertion that his support for a ban on nuclear testing would probably cost him votes, as quoted in As We Knew Adlai : The Stevenson Story by Twenty-two Friends (1966) by Edward P. Doyle, p. 185

The Way Some People Die (1951)

The Atheism Tapes (2004)
Context: Many people do simply awful things out of sincere religious belief, not using religion as a cover the way that Saddam Hussein may have done, but really because they believe that this is what God wants them to do, going all the way back to Abraham being willing to sacrifice Isaac because God told him to do that. Putting God ahead of humanity is a terrible thing.