Earth is seen from space in this recent photo composite image from NASA made over a span of several months and from different angles.
As far as failed predictions go, this one may be the original. Everyone knows the world is round, right? Not so. Homer thought it was flat. Ancient Buddhist cosmology agreed that earth was like a horizontal disk. Hebrew Scriptures suggested it might resemble a dome. Some in ancient China claimed it to be a square. And when Columbus sailed the ocean blue in 1492, many Europeans thought he might reach its edge. Some scholars suggest that a round-earth theory had more early support than one might think. Echoes of a round-earth cosmology can be heard in Plato, and 6th century B.C. Greek philosopher Pythagoras (yep, same a² + b² = c² guy) is said to have agreed. Around the time of Christ, an Asian belief held that the earth was like the yolk in an egg, and Muslim scholars supported a round earth by the 9th century. The Western world joined the round-earth campaign a little late, when Magellan's 1519 global voyage seemed to confirm the round hypothesis. Yet, as is the case with many strange predictions, a handful of believers like the Flat Earth Society still hold fast to their convictions. The rest of us would say however, they are, um, flat-out wrong.