Through a dissection of the theory of product life-cycle and its suggestion of urban decline from disinvestment of outdated industry, Friedrichs attributes the root cause of shrinking cities as the lack of industrial diversification within specific urban areas.
通过剖析产品生命周期理论及其对过时产业撤资导致的城市衰退的迹象，弗里德里希斯将城市收缩的根本原因归结为特定城市地区缺乏产业多元化。