Amazon's recommendations aren't just a computer talking, it's the collective judgment of millions of people acting independently in their own self-interest. Amazon is the biggest and most effective word-of-mouth generator for books because it measures not what people say, but what they_ do._ People don't always recommend their favorite current book to each of their friends and acquaintances. But Amazon factors each buying decision into its recommendations for like-minded customers.
Just as a well-programmed computer can defeat a master chess player, automated recommendations can suggest just the right book, including books that would never occur to a brilliant bookstore clerk, says Amazon chief executive Jeff Bezos:
I remember one of the first times this struck me. The main book on the page was about Zen. There were other suggestions for Zen books, but in the middle of those was a [recommended] book on "How to have a clutter-free desk."
That's not something that a human editor would ever pick. But statistically, the people who were interested in the Zen books also wanted clutter-free desks. The computer is blind to the fact that these things are dissimilar in some way to humans. It looks right through that and says, "Yes, try this." And it works.1