One day, a traveler came to Joshu's monastery bearing an ancient map. The map showed verdant forests, majestic mountains, winding rivers. And Joshu said, "do we not live in a wondrous world, that has such terrain features in it?"

The traveler frowned. "This we do not know! All we can say is that when we travel to these places, it looks as if there are forests, it feels as if there are mountains, it sounds as if there are rivers. Geography deals not with the land, but with what we can say about the land. The rest is poetry, religion, metaphysics."

Joshu went to the other room to fetch a scroll, and inscribed on it a crude schematic representation of the map the traveler brought. He then wound the scroll up and used it to beat the traveler over the head. At that moment, the traveler was enlightened.

Not content with the emptiness of mere talk,

he prefers to talk about talking.

Does he not know that to take one step back

is to slide into the abyss?

Strictly speaking, knowledge doesn't need to have predictive power, as your utility may depend on a piece of knowledge, in which case you don't expect to observe anything else differently, but you prefer to act differently. That knowledge fixed in a belief still pays rent, but not in expectation.