At least in the last 40 years of that graph, recessions seems to be it. A recession hits, some people get fired (sticky wages, etc, etc), the recovery comes an

At least in the last 40 years of that graph, recessions seems to be it. A recession hits, some people get fired (sticky wages, etc, etc), the recovery comes and it's cheaper to automate stuff than hire people. Then things coast for a while. The cost of automation keeps falling, people keep getting relatively more expensive, but in good times generally you don't get people getting fired en masse because times are good and the employer is making a profit anyway. Then a recession comes, and the cycle repeats...