People keep spending additional units of a particular resource on a want until their marginal benefit is not affected by their marginal cost. Marginal benefit has to do with how much utility one gets from an additional unit of a good or service. On the other hand, the marginal cost has to do with how much one spends (not just money) for an additional unit of a good or service. In general, people keep adding units of a particular resource while the marginal benefit (utility) is greater than or equal to the marginal cost. In other words, the marginal utility is worth the marginal cost. However, when the marginal benefit is less than the marginal cost for a given good or service, consumers will see the marginal utility as not worth the marginal cost. In other words, consumers perceive that what they pay (marginal cost) is more than what they receive (marginal benefit). In some cases profit can be maximized when the marginal cost equals the marginal benefit.
