 Paul Rosenstein-Rodan spoke of a similar concept called "indivisibility of demand" which hypothesises that if large investments are made in a large number of industries simultaneously, an underdeveloped economy can become developed due to the phenomenon of complementary demand.However, both Nurkse and Rosenstein-Rodan only took into consideration the situation of industries that produce complementary goods.There are substitute goods too, which are in competition with each other.