When some steps of a complex, multi-step task are automated, the demand for human work in the remaining complementary sub-tasks goes up. In contrast, when the task is fully automated, the demand for human work declines. Upon aggregation to the macroeconomic scale, partial automatability of complex tasks creates a bottleneck of development, where further growth is constrained by the scarcity of essential human work. This bottleneck is removed once the tasks become fully automatable. Theoretical analysis using a two-level nested constant elasticity of substitution production function specification demonstrates that the shift from partial to full automation generates a non-convexity: humans and machines switch from complementary to substitutable, and the share of output accruing to human workers switches from an upward to a downward trend. This process has implications for inequality, the risk of technological unemployment, and the likelihood of a secular stagnation.

当复杂的多步骤任务的某些步骤被自动化时，其余互补子任务对人工的需求就会上升。相比之下，当任务完全自动化时，对人工工作的需求就会下降。聚合到宏观经济规模后，复杂任务的部分自动化造成了发展瓶颈，进一步的增长受到基本人类工作稀缺性的限制。一旦任务变得完全自动化，这个瓶颈就会被消除。使用两级嵌套恒定弹性替代生产函数规范的理论分析表明，从部分自动化到完全自动化的转变会产生非凸性：人和机器从互补转变为可替代，而工人的产出份额从上升到下降的趋势。