Determining the Mind of a Main Character
How a character thinks determines the order of Acts within a story.
When looking at the structure of the story, an integral part of its makeup lies within the mind of the Main Character. How they go about solving problems determines the order of the events in the story.
There are two different minds a Main Character typically exhibits--one is based on Linear thinking, the other on Holistic. While a Main Character can employ both styles in the solving of their problems, typically one will be preferred over the other. For the most part these problem solving styles fall along gender lines: male Main Characters will employ Linear thinking, while female Main Characters will employ Holistic thinking. This, however, is not a hard and fast rule and several interesting stories can be found wherein the norm is not the rule (Malcom Crowe (Bruce Willis) in The Sixth Sense being one example of this).
Of Two Different Minds
A character who approaches problems linearly will take actions because of the results they hope to create. If I do this, a Main Character would think to themselves, then this result will occur. They may also think, when this happens, this also happens (pattern-matching). Both represent linear ways of solving problems.
A character who approaches problems holistically will upset the balance of things or try to balance the relationship between things in order to zero out any inequity that may exist. While the male system of perception deals with linear and pattern-matching, the female system of perception deals with the acceleration between things and the rate of acceleration change during that process. It's not as easy to describe as a linear Main Character1, but the difference between the two should be apparent. One is based on space, the other on time.
A character who thinks linearly will take certain actions or make certain decisions first based on that if/then causality. At the same time, a holistic character would take completely different actions or decisions based on the direction they want things to head. Therefore, the difference between the two lies in the order in which those events occur. A linear Main Character might do things in an A,B,C,D order whereas a holistic character might do things in a C,B,A,D order. Two different minds will take two different courses of action.
Although not a part of most conventional story theories, the problem-solving style of a Main Character (what Dramatica refers to as Mental Sex) is every bit as important as the "Inciting Incident" or the Progressive Complications of the 2nd Act. When an Author cares about structure, it is incumbent upon them to understand everything that goes into framing the order of events in a story. How the Main Character goes about solving problems is one part of that foundation.