Nothing clouds your mind like dogma. Dogma can come from an outside authority or it can be self-generated from one's past successes. Here are some examples: None other than Plato himself dictated that the circle was the perfect form for celestial movement, and for the next two thousand years, astronomers said that planetary orbits were circular even though their observations didn't quite jibe with that. Even Copernicus used circles in his heliocentric model of the universe. Only after much soul-searching did Kepler use the ellipse to describe the heavenly paths.

Joseph Semmelweiss, the 19th century Hungarian physician, felt that doctors could reduce disease …