The comfortable story goes something like this. Automation eats jobs from the bottom up. First the farmhand, then the factory worker, then the cashier, and eventually, in some distant and frankly theoretical future, the people with degrees. The more education you have, the higher you sit on the cliff, and the longer it takes the water to reach you. Knowledge workers believed this for about seventy years, which is roughly how long it takes to build a mortgage, a pension, and a personality around it. The story has a second, quieter clause, and it is the one that matters. It...