Original Post
Please note that the following applies only to plot-based games like RPGs and Adventure games. Also, it''s a chunk of my thesis-in-progress, so please excuse the big words - I tried to define them as I went along. This is my theory of why humans create stories and what benefits we get from reading/playing stories.
The human infant enters the world a willing, if not yet very able, mimic. Children mimic the actions of adults, other children, and animals, and they mimic various sounds including those of language. A special mental system referred to as “the human language instinct” kicks in when the child is about two years of age. Suddenly the mimicked “mamama” takes on meaning and becomes “mommy” and demands like “Cup! Cup!” acquire comprehensible form: “I want the cup!” A year later at “about the age of three, … a child begins to show the ability to put together a narrative in coherent fashion.” Another mental system, referred to as “the narrative instinct”, has started working, allowing logical connectors and temporal indicators to show up in the child’s speech. “Jeremy’s bad!” gets elaborated into “Jeremy stole my toy so then I told him he was bad!” This is the same point at which children become capable of pretence and pretend play, which also require an awareness of temporality and causality.
In his Poetics Aristotle asserted that metrical and non-metrical literature were a natural outgrowth of imitation, or mimesis, which both children and adults experienced as a playful act. He says: “It is clear that the general origin of poetry was due to two causes, each of them part of human nature. Imitation is natural to man from childhood, one of his advantages over the lower animals being this: that he is the most imitative creature in the world and learns at first by imitation. And it is also natural for all to delight in woks of imitation. …to be learning something is the greatest of pleasures not only to the philosopher but also to the rest of mankind, however small their capacity for it…. Imitation, then being natural to us – as also the sense of harmony and rhythm - …it was through [mankind’s] original aptitude, and by a series of small improvements [that literature was created].”
And in point of fact, children’s play researchers today believe pretend play and literature to be two similar ways to satisfy the same instinct. Pretend play is essentially a cooperative, spontaneous creation of the same narrative that we, as readers, ingest more-or-less passively: “…in pretend play we witness behavior which moves between mimesis and mythos (story). Play … emerges … as an imaginatively constructed and linguistically realized pathway between simulation and mythologization. From this vantage point make-believe play is social poetry in the making.” Play is poetry, and poetry, play. The two activities are attempts, via slightly different means, to satisfy the narrative instinct.
Much the same remark has been made by those studying fiction and its effects on the unconscious mind: “These satisfactions are only explicable on the assumption that as we read, or sit in the theater and watch, we simultaneously engage in a kind of silent and immobile play. Out of the same impulse which leads a child to gallop about like a horse to find out what it would feel like to be one (mimesis), we act out, of course in sublimated and truncated fashion, the roles and events which interest us.”
And again, the same is true of tabletop roleplaying, computer roleplaying, and computer adventure games, all of which are play/narrative hybrids.
During the past three decades psychologists and linguists worked to puzzle out the shape of the mental machinery that allows sentence generation and story generation. Noam Chomsky is credited with the formulation of the first transformational generative grammar, a “…system of rules capable of enumerating all and only the sentences of the language, and of assigning each sentence its correct structural description.” Thomas G. Pavel then demonstrated that: “…a grammar which generates stories is subject to the same restrictions as grammars for natural-language sentences. Arguments similar to those proposed by Chomsky against regular and context-free grammars can be constructed in order to show that typically narrative phenomena cannot be accounted for by these varieties of formal grammars. Consequently, the grammar adopted here belongs to the family of transformational generative grammars.” In speaking of stories, Pavel is talking about narrative constructions, defined thus: “Narrative is the representation of at least two real or fictive events in a time sequence. The events must be related but neither can presuppose or entail the other. Narratology (the application of transformational generative grammatical patterns to narrative constructions) is the study of the form and functioning of narrative. … Narratology examines what all narratives have in common and in what ways they are allowed to differ.”
The use of transformational generative grammar to model story generation called for a more complex theory of memory than had been necessary to explain sentence generation. “Script theory” evolved to fill this need. According to script theory, all memory is organized around primitive categories of personal experience, called “scripts” or, elsewhere, “thematic core concepts”. Specific memories are stored as pointers to scripts, with appropriate specific details appended. Thus, the memory of reading a book would be stored as: (primitive category = I got visual information and put it into long term memory.) + (details = The book was about a white whale; I thought it was really boring.) Scripts allow individuals to make inferences needed for understanding by filling in missing information. Note that only a narrative sequence of events, that is, one event following another related event (e.g. receiving and then storing visual information) can be stored as a script.
This theory of memory is supported by the fact that scripts are consistently found to determine the pattern of events described by the narrative in both children’s pretend play and the literature of older children and adults. Children’s pretend play is generally based on one of three basic scripts: separation-reunion, threat-neutralization, and deprivation-provision. Common variants of these include, for separation-reunion: death-rebirth, object lost-object found, person absent-person present; for threat-neutralization: danger-rescue, villain present-villain defeated, injury-healing; and for deprivation-provision: food deprivation-food provision, care deprivation-care provision.
There is currently no agreement on how to enumerate the scripts found in literature and plot-based games, but one of the more popular and enduring systems of classification is Georges Polti’s 1868 postulation of the Thirty-Six Dramatic Situations. These follow the narrative form necessary to a script because each problem situation stated is assumed to be followed by a resolution of that problem. The thirty-six scripts are: supplication, deliverance, revenge, vengeance by family upon family, pursuit, victim of cruelty or misfortune, disaster, revolt, daring enterprise, abduction, enigma, obtaining, familial hatred, familial rivalry, murderous adultery, madness, fatal imprudence, involuntary crimes of love, kinsman kills unrecognized kinsman, self-sacrifice for an ideal, self-sacrifice for kindred, all sacrificed for passion, sacrifice of loved ones, rivalry between superior and inferior, adultery, crimes of love, discovery of dishonor of a loved one, obstacles to love, an enemy loved, ambition, conflict with a God, mistaken jealousy, faulty judgement, remorse, recovery of a lost one, loss of loved ones. While variations of separation-reunion and danger-rescue remain popular (e.g. obtaining and disaster), depravation-provision is no longer an issue, and authority, love, morality, mistakes, and sacrifice have become new basic scripts.
While several scholastic communities were discovering how we narrate and what we narrate about, another two were trying to figure out why we want to narrate in the first place. As Simon O. Lesser, pillar of the community investigating fiction and the unconscious, puts it, “…the very first subject we should consider is what needs impel us to engage in such an activity as reading about the imaginary doings of imaginary people.” The reader-response criticism community thought they knew: it was purely a side effect of the mimesis instinct, whose purpose was to reward us for learning about our world, gathering information necessary to survival. A typical statement of this idea is:
“The fact is that every time we open the pages of another piece of writing, we are embarked on a new adventure in which we become a new person – a person as controlled and definable and as remote from the chaotic self of daily life as the lover in the sonnet. Subject to the degree of our literary sensibility, we are recreated by the language. We assume, for the sake of the experience, that set of attitudes and qualities which the language asks us to assume, and if we cannot assume them we throw the book away.”
Aristotle thought that while exercising the mimesis instinct was the original reason for literature, literature had evolved to also provide emotional catharsis. This evolution was the cause of the first split of literature into genres, specifically comedy and tragedy. Aristotle lists one of the essential ingredients of tragedy to be “…incidents arousing pity and fear, wherewith to accomplish the catharsis of such emotions.” He explains: “…not every kind of pleasure should be required of a tragedy, but only its own proper pleasure.” And he presumably said much the same thing about comedy accomplishing the catharsis of hilarity. That portion of the poetics is lost, but the Tractatus Coislinianus, assumed to be notes taken by a student being instructed in the Poetics before that portion was lost, mentions “…pleasure and laughter effecting the purgations of the like emotions.”
Lesser, working from Freudian roots, added, “We read fiction to secure richer fulfillment of desires no more than partly satisfied by life, and to allay the anxieties and guilt feelings our life experiences arouse.” The allaying of anxieties and fulfilling of needs function, he explains, because, “While fiction alters the facts of experience, a fundamental purpose of those alterations … is the achievement of an imaginary world more lifelike than life itself, more directly and honestly concerned with essential problems, more supple in its expression of every aspect of man’s nature, less burdened by distracting irrelevancies. Undoubtedly many of the alterations are made at the behest of the pleasure principle: the world of fiction is more gratifying and less fearful than the world of experience. (Excepting the worlds of horror stories.)”
Brook summed up all these reasons to read and concluded that narrative is the major way every human relates him- or herself to the world. “Our lives are ceaselessly intertwined with narrative, with the stories that we tell and hear told, those we dream or imagine or would like to tell, all of which are reworked in that story of our own lives that we narrate to ourselves in an episodic, sometimes semi-conscious, but virtually uninterrupted monologue. We live im-mersed in narrative, recounting and reassessing the meaning of our past actions, anticipating the outcome of our future projects, situating ourselves at the intersection of several stories not yet com-pleted.”
In addition, pretend play and multiplayer plot-based games satisfy our drive to socialize, and plot-based games fortify our self-confidence by convincing that we are successful competitors.
If you actually made it through reading all that, congradulations! 
The point, as it applies to game design, is that, knowing what our psychological benefits our players expect to gain from experiencing our games, we should strive to design games that are psychologically satisfying.
The point, as it applies to game design, is that, knowing what our psychological benefits our players expect to gain from experiencing our games, we should strive to design games that are psychologically satisfying.
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