In order to societies to reap the gains from trade, it is necessary to

Consider a lake stocked with fish. The total value of fish caught at the lake depends on the number of fishers, as shown in the accompanying table. As the table indicates, 1 fisher can catch $36 worth of fish in a day, 2 fishers can catch a total of $66 worth of fish, 3 fishers can catch a total of $90 worth of fish, and so forth. The fishers are identical, and the opportunity cost of a day at the lake is $18 for each fisher.

(i) Complete the table by calculating the value of each fisher's catch, on average, and the social marginal benefit of the lake.
(ii) If use of the lake is nonexcludable, how many fishers come to the lake? What is the total value of their catch? What is their total cost? What is the social gain from the existence of the lake?
(iii) What is the optimal number of fishers at the lake? What is the social gain if this optimum is achieved?
(iv) What entrance fee would lead to the optimal outcome?

"Mediocre economists often consider only the immediate direct effects of a change, whereas a good economist will also consider indirect effects that may only become observable over time." This statement most clearly emphasizes

What will be an ideal response?