When you pick a single Concern, you limit the other throughline Concerns to the same position in the quad. When you pick a Concern, you also limit the Domain / Throughline above it.
Dramatica is organized like four different pairs of glasses (perspectives) looking at the same inequity. Each pair of glasses distorts the view differently because they're looking from different places--kind of like the blind men describing an elephant. Each one describes what he sees and comes to different conclusions because of the limitation of their view (one feels the trunk and thinks it's like a snake, another feels the leg and thinks it's like a tree, another feels the ears and thinks it's like a fan, etc.). All of the are partially correct, but also incorrect in their conclusions.
The four domains work in a similar fashion. When we look at the Concerns, for example, the Past is similar in its relationship to a Situation as Memories' relationship is to Fixed Attitude. They aren't the same thing, but are similar in nature within its own context.
Every time you choose an item in one throughline, you limit (and sometimes pick) other choices in the remaining throughlines. This is what keeps the "argument" you are making consistent. Comparing apples to apples, so to speak.