To get what they want, the fool must reverse their circumstances and move from selfishness to selflessness. This can rarely happen while trapped in the grind of regular life, so in traditional comedies, the fool must move to a place where the rules of life are different. In classic comedies from the Greeks to the Renaissance, the fool moves from the city into the forest, known as "the green world" for obvious reasons. Yet the green world is not just a forest--it is any place marked by reversal--what is unacceptable in the city is acceptable in the green world, what is difficult becomes easy, and what is foolish becomes wise.
Few modern comedies force their characters into a literal new place, but the spirit of the green world still exists in that characters are thrust into new situations or relationships that make their regular life seem strange. Usually this is achieved by a character challenging the fool to reexamine how they live life. This could be a romantic interest, coworker, or child--a trope for the past 15 years that accomplishes this is the manic pixie dream girl. The green world, either literal or figurative, is a place of change where anything can happen.