One of the effects of the digital age is that it's pretty easy to write and "publish" a book. There's no shortage of books. What there's a shortage of is GOOD books.I don't believe the world is suffering from not enough people reading "Harry Potter and the Tired Conclusion," however we probably would be better off if more people read, say, "The Road to Serfdom."
I like Eric's answer.I'll add that this isn't a Supply & Demand question. Every writer reads her book, ergo the number of books read to written is always at least 1:1. I posit it is impossible to write a book without reading it.
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