It is necessary not only that capital be accumulated, but also that it be mobilized for productive use, if an economy is to benefit from an increase in capital per person. The classical model of resource allocation assumes that within any economy capital is perfectly mobile. It implies, therefore, that once allowance is made for uncertainty and risk, returns on investment are equal in all industries in all regions. Such a model, while logically consistent, is not very useful for analyzing the process of economic growth. In the early stages of development, because the uncertainty discounts are high, capital is not very mobile. As a result, rates of return vary widely between industries and between regions; and growth in high-interest regions is retarded. Development, in part then, takes the form of a reduction in uncertainty discounts—a reduction that makes it possible for capital to move more freely between regions and industries.