Final answer:
The adage, 'There is no such thing as a free lunch,' illustrates that people face tradeoffs because resources are limited and every choice has a cost.
Step-by-step explanation:
The adage, "There is no such thing as a free lunch," is used to illustrate the principle that people face tradeoffs. In economics, tradeoffs refer to the choices individuals or societies make when they give up something in order to obtain something else. Every choice has a cost because resources are limited, and people cannot have everything they want. For example, in the scenario mentioned, a restaurant that gives away free appetizers has to recover the cost by raising prices for other customers. The idea behind the adage is that even when something appears to be free, someone always has to pay for it in the end.