A programme, organization or activity, or individual and collective human development potential, may be limited either by internal or by external limitation, or by both. Internal limitation may be inherent, constituted by the very nature of human organization and individual and systemic capacities. Thus a primitive society may organize healing functions via ritual, shamanism, witch doctors and other activities; but without real medical knowledge it is nonetheless completely exposed to disease. Internal limitations may also be accidental or circumstantial. It can be said, for example, that inadequate medical services in developing countries can be remedied by training indigenous peoples in medicine, assuming there is no insurmountable intellectual or cultural obstacle to this education. Extrinsic or external limitations may be illustrated by the isolation of a community so that it cannot participate in medical advances. Such a limitation may be presented by natural circumstances. Other external limitations may be imposed by human activity, for example, economic or military subjugation of peoples so that their medical needs are not met.
Whether in natural or human resources, there is a point beyond which "more" is really not feasible at a given time. This applies not only to the limits of natural resources available to be exploited on the planet, but also to the capacity of urban areas for expansion, of industries for growth, of individuals for rapid change. Although it is well to avoid drawing false limits to living out of a feeble imagination or weak faith, it is equally foolish to pretend that existence is an inexhaustible well.
The concept of limitation illustrated in dressed-up but simplistic supply and demand models is frequently expressed by arbitrary numbers in both sides of the equation. They are arbitrary because there is no scientific knowledge that is incontrovertible and that provides a 100% accurate forecasting basis. In addition, applied science (that is, human technology) keeps pushing back the limits. For example, the diminishing resources of this planet may be augmented by resources on other planets. Human intelligence is being augmented already by computer artificial intelligence. And human development itself may go beyond its present limits by the employment of behavioural re-education, by genetic engineering, and by new forms of political and social organization developing in a new age.