What principle states that increasing one aspect of production while keeping others constant will eventually decrease overall return?

The principle that states that increasing one aspect of production while keeping others constant will eventually lead to decreased overall returns is the Law of Diminishing Returns. This concept is fundamental in economics and production theory. It suggests that as you continue to add more of one input to a production process—such as labor or capital—while holding other inputs fixed, there comes a point where the incremental output or 'return' from that additional input begins to decline.

For instance, in a manufacturing scenario, if you keep adding more workers to a factory that is limited in space and machinery, initially, productivity may increase significantly. However, after a certain point, the factory becomes overcrowded, and each additional worker contributes less and less to overall production—the returns on adding more workers diminish.

This principle highlights the importance of efficiency and the balance of all production factors, helping businesses make informed decisions about resource allocation and maximizing output without overextending any single input. The other concepts listed, such as market equilibrium, the demand curve, and price elasticity, deal with different aspects of economic theory and do not specifically address the relationship between production inputs and their returns.