In contrast to Prerequisites, Preconditions are like riders tacked on to the ends of bills voted on in Congress. With such a bill, the Goal might be to help an endangered species. One of the Requirements would be to pass a bill that gives the species legal status as endangered. One of the Prerequisites would be to get enough votes to pass the bill. One of the Preconditions for getting a block of votes would be to add a rider on the bill that provides subsidies to the tobacco industry. Clearly the rider has nothing to do with the original bill, and might even be philosophically at odds with its intent. But, to get the job done, concessions must be made.

Similarly, Preconditions in a story are non-essential constraints or costs placed on the characters in exchange for the help of someone who controls essential Prerequisites. This might be the only Bedouin who can supply camels so an expedition can cross a desert, who insists they take his uncontrollable daughter with them.

In the movie, The Karate Kid, the Protagonist is a young boy who wants to be a Karate champion. To achieve this goal, he must meet the Requirements of winning preliminary bouts. To win these bouts, the Prerequisites are that he receives extra training from a master. The master, who controls this Prerequisite, adds a precondition. He insists the young boy learn new moves by doing chores around the master's house that incorporate those moves, "Wax on... Wax off." Clearly, there are other ways to learn Karate than doing chores, but this Precondition comes from the master's desire for the boy to learn humility with his skill.