Think of the last two major things you bought. Why did you buy them? What were your opportunity costs in making the purchase? What would have been the opportunity cost, if you had NOT made the purchase? (Not all opportunity costs are measured in money.)
b. Did those selling them to you provide the goods because they cared about your needs? What was their REAL motivation?
c. When you go to work, why do you "sell" your labor to that organization? Do you really care what the owner of the organization really wants? d. How do questions b. and c. relate to Adam Smith's statement from The Wealth of Nations: "It is not from the benevolence of the butcher, the brewer, or the baker that you expect our dinner, but from their regard to their own interest?