People keep spending additional units of a particular resource on a want until their marginal benefit is their marginal cost

Marginal cost refers to the amount of money it cost a company to produce one more of a particular product while the marginal benefit refers to the benefit that is obtained as a result of producing that one extra product. Profit is maximized when the marginal cost equals the marginal benefits.

answer; validity;

stable food supply,social structure, government,religion,culture/art,technology and writing/language;