Why The Main Character's Approach
The central character of a narrative focuses their initial efforts on the source of their personal problems.
Main Characters make decisions and they take actions. They engage in deliberation and they get things done. Yet for some reason, Narrative Science seemingly requires both Analysts and Authors to force their Main Characters into choosing one or the other.
Referred to in Dramatica (the first version of Narrative Science) as the Main Character Approach, this story point files the great characters of literature and the silver screen into two boxes: Do-ers or Be-ers. The former act first then ask questions later, while the latter first internalize before then making their move. Limiting and reductive at first glance, the reason for this determination lies in a better appreciation of the mind's problem-solving process and its place within the structure of a compelling and meaningful story.
A Place to Begin
Functioning stories exist as models of human psychology--in particular, the process of problem-solving. One of the first steps to take when solving a problem lies in determining exactly where to place one's effort while attempting resolution. Should I try to change the world around me or should I try to change myself? Answering this question initiates the process of problem-solving. Ignoring it ignites the process of justification (or hiding the problem from ourselves).
Problems don't exist outside of us, nor do they exist within us--rather, they exist in the area between us and our environment. Because we can't address that inequity directly, we must focus our efforts on one area or the other--thus, the Main Character's Approach.
When faced with internal issues we focus on ourselves. When faced with external issues we focus on our environment. Why? Finding internal solutions for internal problems is much easier than searching for external ones. Likewise, exploring external solutions for problems within the external environment becomes a much easier task than searching for an internal one.
This Approach often shows itself as a preference on behalf of the Main Character. Do-ers prefer to do the work outside, Be-ers prefer to do the work inside.
The Path of Least Resistance
A Main Character facing personal issues growing from an external state of affairs or an external activity will approach their problem first by taking action. As a poor playwright with nothing to show for his efforts, William Shakespeare (Joseph Fiennes) searches externally for a new muse in Shakespeare in Love. Hogarth Hughes (Eli Marienthal) from The Iron Giant seeks adventure and action from a life that has neither.
Conversely, a Main Character experiencing personal issues emanating from an internal attitude or dysfunctional way of thinking will approach their problem first by modifying their behavior. Sully (John Goodman) from Monsters, Inc. finds his greatest asset--fright--to be a behavior in need of change if he is to ever grow closer to Boo. Meanwhile "Deanie" Loomis (Natalie Wood) from Splendor in the Grass attempts to re-wire her behavior--even going so far as to accept institutionalization--in order to keep from slipping further into madness.
In each of these cases, the Main Character approaches their personal problem by first taking that path of least resistance. External takes external, internal takes internal. Realizing this, one can easily see how the Main Character's Approach can be used to identify the source of that central character's personal problem as well as their response to it.
Assuming the Right Perspective
Key to pinpointing the source of these personal problems remains an accurate account of point-of-view. Are we taking a first person perspective or are we looking at it from a distance? Is the inattentive parent on the bus letting their child run rampant out of neglect, or is it because they've just received devastating news that they're to raise the child on their own? One can't can't asses inequity without first taking into account perspective.
Same with story.
The examples of story given above focus on the issues facing each of those Main Characters personally. They may have other concerns within the larger picture or within other relationships, but when it comes down to dealing with my problems, and what am I facing (as required by the Main Character perspective) that first-person point-of-view becomes all important.
Creating a Mind for the Audience
It isn't as if Main Characters can't both Do and Be within a story. The concept of Main Character Approach certainly allows for well-rounded characters exhibiting both qualities. But the end-game can't become a quest to capture down on paper "real people".
Approach plays out as a preference because stories do not replicate real life. Rather, stories exist as constructs designed to communicate meaning by creating a "mind" for the Audience to possess. The Main Character represents the first-person perspective of this mind and thus, from that point-of-view sees the problem as being either internal or external (because it can't see that true problem in-between the two). Taking the path of least resistance this story-mind approaches that problem by tackling external problems with actions and internal ones with behavior modification.
Why then ask for the Main Character's Approach during the course of crafting a story? In answering that question, one can help solidify the Audience's position within the mind of a story while simultaneously granting clues as to the work and effort put forth by the Main Character to resolve their personal issues.