Which means they don’t surprise us. They don’t take us out of our comfort zone. A recommendation engine isn’t the spouse who drags you to an art film you wouldn’t have been caught dead at but then unexpectedly love. It won’t force you to read the 18th century canon. It’s no substitute for stumbling onto a great CD just because it has cool cover art. Recommendation engines are the enemy of serendipity and Great Books and the avant-garde. A 19th century recommendation engine would never have said, If you liked Monet, you’ll love Van Gogh! Impressionism would have lasted forever.