On Monday I talked a lot about how a character's Decision-Making Paradigm (that is, their Worldview and their Philosophy) dictate how they see things and what actions they think are positive or desirable in any given situation. Which is all fascinating, but it's all terribly abstract and kind of hard to apply. Because not all of us are crazy writer-people with mountains of time on our hands and the ability to plot out the philosophies and worldviews of different characters before we even start writing.
And you're absolutely right. No one has that kind of time in the modern age, and even if we did have the time for that kind of craziness, it would be unrealistic to expect a writer to have that level of detail plotted out, even for the major characters in a given story. It's just ridiculous.
So how does all this translate to how we tell stories and how we write?
I think it all boils down to awareness. When writing a scene where two characters are in disagreement, take a moment to ask yourself why. Why are they thinking this way? What could make this decision make sense? Chances are, if it doesn't make sense to you, it won't make sense to y our readers, either, and they'll wonder what your're trying to say with this unbelievable or undesirable decision.
For example: In a book I read recently, one of the major points of interest was that a certain character's decisions didn't make sense. He would act one way, then another, and there didn't seem to be any rhyme or reason to it. While it isn't necessary for a reader to understand all of a certain character's choices, it is remarkably important for those choices to be consistent with the character that made them.
In this case, to make this paradox of a character acting in ways that are inconsistent a point of interest, it would be narratively inept to then leave this conflict unresolved. I shall call this an "external conflict," as it is a conflict between the narrative and the reader, rather than a conflict between characters or situations within the narrative itself.
But when the conflict is narratively internal - that is, within the story - then there are portions of this conflict that do not need to be explained, just as there are elements of the setting that never need to appear "on screen," because they're not important to the reader.
So to sum this up:
Let's say you're writing a scene in which two characters in a situation at the same time disagree on how the situation should be dealt with.
Rather than choosing the most "interesting" argument for them to have, instead take a look at what the characters have said and how they've behaved up to this point. Ask yourself what those choices and those words have had in common. What makes them all part of the same pattern, rather than a collection of random but narratively convenient actions.
It would be nice, of course, to do this the other way around, by figuring out how a character makes decisions first and then put them through interesting problems, but that's not the way human minds work. We are accustomed from infancy to knowing other people through their actions and figuring out their priorities from the outside. This, too, is how we get to know the majority of our characters, and so the world turns and we continue to make up interesting stories.