When Democritus proposed that the universe is composed of atoms or when Ibn Kahldun theorized that humans came from a gradual, generational transformation of monkeys they were both astoundingly correct. Both ideas turn out to be true, but both are in some ways simply lucky. Today we admire these men and their ideas because we value are ideas in the marketplace of evidence and it so happens that today we have mountains of evidence backing up both of these claims. This hasn't been the case for most of history. When these ideas were proposed they were not competing in a marketplace of evidence, they were competing in the marketplace of truthiness. Truthiness, a brilliant word gifted to us by the great Stephen Colbert, being exactly that quality of an idea that makes it feel true without the need for any evidence backing it up. 

While the theories of Democritus and Kahldun gained a degree of acceptance in their time, along with a degree of infamy, they were both eventually reduced to footnotes of history precisely because, while considered interesting, their truthiness value was low. It was only when humanity began shopping for ideas based on the quality of evidence that these theories were rediscovered and received the success they deserved. That shift of marketplaces, when humanity decided that an idea must be tested against the world and not just within the confines of our own minds, was one of the most momentous and beneficial in our history. But the old marketplace didn't go away. It's still there, and we must always be wary of those attempting to bring us back to the old and shiesty bazaar of mere believability.