The document discusses marginal costs and benefits and how they can be used for decision making. It defines marginal benefit as the change in total benefit from an action and marginal cost as the change in total cost from an action. It states that people are better off doing more of an activity as long as the marginal benefit exceeds the marginal cost, and better off doing less of it when the marginal cost exceeds the marginal benefit. An example compares the marginal benefit of exercise to the marginal cost of reduced study time.