4. The demand for a product indicates the intensity of consumers' desire for the item.

The (opportunity) cost of producing the item indicates the desire of consumers for other goods that must now be foregone as a result of the use of resources that were required to produce the item. In a market economy, these two forces-demand and costs of production - balance the desire of consumers for more of a good against the reality of scarce resources, which requires that other goods be foregone as more of any one specific item is supplied.