Dramatica : Every “Act” in a four-act structure, is not really descriptive of an activity, but is a sign post on the path of that throughline. If your Act I for your Obstacle Character is Progress, then it means they are starting at Progress. In other words, when we come to them at the beginning of the story, Progress best describes the principal area of their efforts and concerns. For an Obstacle Character, we measure them most by their “Impact” as opposed to what they, themselves, are paying attention to.
So, the Obstacle Character’s impact concerns “Progress” in Act one. But that is just where they start. Their impact shifts from Progress to Future. That is really what the first act of the three-act structure is all about. The OC’s impact “shifts” from Progress to Future over the course of the act. When the OC’s impact is fully on the Future, that is where we feel an “act break” in the story. Now, an impact on Progress, simply means that the OC is having an effect on Progress, everywhere they have an influence. They might be speeding up Progress, or slowing it down. Whichever way the impact, depends upon what is needed to ultimately bring the Main Character to consider changing their approach.
By impacting Progress, the Obstacle Character forces the Main Character into a position where they must abandon their approach in one area, and therefore, by the end of the act, the Main Character has “grown” a little closer to addressing the central issue of the story… the Obstacle Character has forced them to grow a bit, in order to avoid having to deal with that issue right here and now.
But as soon as the Main Character thinks they can relax, the act changes, and the OC’s influence can be felt in a new area; Future. Future is just the thing that will force the main Character forward in their growth to that ultimate decision to remain steadfast or change. And, Future will be able to do that without allowing the MC to back slide to where they started. It is important to keep in mind, that the OC may not even be aware of their impact on the MC. They might, of course, but they don’t have to be.
Sometimes just their presence can force the Main Character to address issues they would rather not. And by their continued presence, as the OC changes their relationship in response to the overall story, their impact changes in just the right way to keep forcing that MC closer and closer to the reason they feel impacted at all. Then, the MC will ultimately be changed, or remain the same, whether that happens in a “leap of faith”, or in a subtle way, where the audience sees that the MC has been changed, but the MC just grows into that change: they never make it consciously. Well, that should open up some questions…