The Nature of Costs: Any discussion of costs in any economics course needs to start with the fundamental idea that it is opportunity costs that matter in decision making.  In addition, it is crucially important to drive home the point that opportunity costs are NOT the same thing as implicit costs.  This error is made in a large number of textbooks (not this one) and it typically comes up when trying to explain opportunity costs in an example.  The typical scenario involves calculating the costs associated with attending university for a year.  The cost obviously includes explicit things like tuition, room and board, textbooks, etc., but it includes implicit costs such as lost wages.  All too many textbooks will say something like “the total cost of attending university is the sum of tuition, books, and the opportunity cost of your time.”  This is true in some sense, but it leaves the impression that explicit costs are somehow not opportunity costs as well.  They surely are, and students should either be reminded or corrected so that they understand this point.