The paraphernalia problem
Imagine you're a teenage boy sitting in your room, a pipe on the bedside table. Your mother knocks, and comes in just as you realize the pipe is sitting out, and she's asking whether you might have that CD she lent you lying around somewhere in the room. So your goal now becomes two-fold: you want to keep her away from the pipe, and you want to find the CD, and each becomes a constraint from the perspective of optimizing for the other.
It's this situation of nuanced multi-goal interaction that is, in my opinion, most usual of interaction broadly. It is neither "adversarial" nor "cooperative" in any pure sense. You are working together, but you are also working against one another—after all, she has a general goal running to "be a good parent" and that goal likely includes crashing high school drug habits.
And if we generalize the scenario a bit, we see that all the basic dynamics are also true of interactions where one conversant wishes to hide some information (parts of the story he is telling, or subject he is being interrogated on, that would make him look bad), and thus to steer the conversation vaguely away from sub-topics, questionings, lines of inference which would bring out these details, force him into a corner—to admit or to lie, either of which carries risk, i.e. cost.
Or of situations where both interactants want to make a decision together, but one has hidden preferences which he wishes to steer the decision-making process towards away from.
Or of situations where one party (say, the teacher) has a set of goals, some of which overlap with student goals.
Etc etc
Sidenote—I think it could be easy to mischaracterize the goal of finding the CD, that because it gets her out of the room, it is merely an instrumental or mediational goal to find the CD. But when an instrumental goal is committed to, even if only for the short-term, it provisionally becomes a terminal goal. If you alter this thought experiment so that you and your mother walk into the room together, both seeking to find an object, and you on the side, trying to steer her away from an object, where finding the searched-for and punishment-invoking objects are equally commensurate in value— little of practical value is altered.