A child learns that birds are named. And enthusiastically asks the elder: "What bird is that? And that? And that?".
He sees many birds, he hears the names, and he is satisfied. Birds have names.
On a different outing, he asks again and gets the answer: "It is a Treesitbird".
He becomes less satisfied. This Treesitbird does not look like the other Treesitbirds. And the other Treesitbirds are not alike either, come to think of it.
That is when the child learns that the elders do not know all the answers. A bird that sits in a tree has a name, but not one the elder knows.