At the heart of science is an essential tension between two seemingly contradictory attitudes -- an openness to new ideas, no matter how bizarre or counterintuitive they may be, and the most ruthless skeptical scrutiny of all ideas, old and new. This is how deep truths are winnowed from deep nonsense. Of course, scientists make mistakes in trying to understand the world, but there is a built-in error-correcting mechanism: The collective enterprise of creative thinking and skeptical thinking together keeps the field on track.

- Carl Sagan