This fairly ordinary passage in Carl Sagan's Broca's Brain ends with perhaps the most famous of all comments ever made about critical thinking. Sagan is speaking of an organization, and a committee, seeking to provide some focus for skepticism on the border of science:
… The committee has also made official protests to the networks and the Federal Communications Commission about television programs on pseudoscience that are particularly uncritical. An interesting debate has gone on within the committee between those who think that all doctrines that smell of pseudoscience should be combated and those who believe that each issue should be judged on its own merits, but that the burden of proof should fall squarely on those who make the proposals. I find myself very much in the latter camp. I believe that the extraordinary should be pursued. But extraordinary claims require extraordinary evidence.