The problem is that the new job titles we keep inventing require ever-greater degrees of intelligence, while the distribution of human intelligence has been remaining just about the same.

A hundred farm workers get replaced by one tractor, but that's okay, because those hundred workers become tractor repairmen, tractor factory workers, tractor designers, and we can farm far more land and produce wealth more efficiently. But not everyone who could plow a field can design a tractor. A thousand years ago, damn near every job was manual labour and could be done with a two-digit IQ, but we're reaching the point in first-world countries where less than half the work which needs to be done can actually be done by someone in the lower half of the population's intelligence distribution.

If we're not there yet, we will be soon. And I think it's fundamentally different to every previous automation revolution.