1. Amazon uses good ML techniques, and they don't work. A good friend of mine worked on the recommendation engine ML side for AMZN until fairly recently. His

1. Amazon uses good ML techniques, and they don't work. A good friend of mine worked on the recommendation engine ML side for AMZN until fairly recently. His review was that it's worse, and more expensive, than having hired people do it by hand. But the sibling comment is more correct -- all three of these things are currently the case.