An analogy on book reading from How to Read a Book - Adler & Doren.

It greatly expresses the relation between writer and reader is remarkably similar to the relation betwen pitcher and catcher in baseball. Both activities of pitching-writing and catching-reading are active, and demanding efforts. There is no such thing as passive catching or passive reading.

The whole activitiy success is how well they cooporate. It's not a win of the pitcher-writer throw a difficult ball but the catcher-reader unable to catch it. Neither if the pitcher-writer throw an easy ball but the ball won't pass the batter (in the case of reading, the batter would be boredom).

The pitcher-writer and catcher-reader are two persons with different level of expertise. Careerwise speaking, they always practice to level up. But it won't be optimal of the disparity in levels are too far. The pitcher-writer normally would always try to throw the most challenging balls as possible.