I think "birds migrate" is a good contender for one of the most startling "humanity discovered that <i>when</i>? and they thought <i>what</i> instead? And it took <i>what</i> to disprove it?" factoids: <a href="https://en.wikipedia.org/wiki/Bird_migration#Historical_views" rel="nofollow">https://en.wikipedia.org/wiki/Bird_migration#Historical_view...</a> <a href="https://en.wikipedia.org/wiki/Pfeilstorch" rel="nofollow">https://en.wikipedia.org/wiki/Pfeilstorch</a><p>It seems so simple and common sense and everyday. It doesn't involve microscopic lifeforms or planets or stars, just... birds. "Where do birds go during the winter? Well, birds are good at flying away from hunters or other bad things. That's why they fly. So maybe they just fly somewhere else. I look up in Fall and I see flights of birds flying in a specific direction. And people in other areas say birds arrive from elsewhere for a while. What else would they do? Turn into little fish and hide in the water all winter, or spontaneously regenerate out of random little clams? Anyway, here's a bird with a big old Central African spear stuck through its whole body who managed to fly here alive anyway which proves that."