In 1930, Pluto was declared the ninth planet. In 2007, it was demoted to "dwarf planet" status by astronomers after considering new evidence. There are now only eight planets.
Also in the 1930s, the ideas of John Maynard Keynes came of age. In spite of a massive amount of evidence that these ideas don't work, unlike astronomers, economists won't demote Keynes's theories to the dustbin of history.