At the beginning, the false agreement might be quite intact. As the story goes along, each event breaks down this agreement. By the end, even the character must see that it's not real. By the end, there is a new realization.
What are some false agreements in story?
In Janet Fitch's novel White Oleander, the false agreement is that the narrator, a teenage girl, believes she can help her mother stay out of danger. This proves false when the mother decides to kill her boyfriend and ends up in prison, abandoning her daughter.
In Jeanette Walls's memoir The Glass Castle, the false agreement is that the narrator, a young girl, believes that her crazy family is eccentric but normal. This falls apart as the parents take more risks and put the girl in danger.
In Lief Enger's novel Peace Like a River, the false agreement is that justice can prevail--when a young girl is attacked by boys in town and her brother defends her, his family can bring him back into the family. Proven false when the brother runs away and aligns with a serial killer.
A false agreement will always be revealed as false by the end of the book. It may be accepted, then denied, then accepted again during the story--humans rarely travel a straight line in growth--but it is exposed by the end for what it is. Even if the character ends up in permanent denial, the reader has seen the agreement as fully false.
Most writers start by describing the status quo that the story starts with. What does everybody put up with, to get along? What are the accepted beliefs?
Some examples of false agreements from different books I've read lately:
2. If I protect my sister, she won't be abused.
3. If I go there in person, I can find the truth.
4. If I keep silent, nobody will get hurt.
There are hundreds of possibilities, and yours will be unique. The "hook" of your story starts from this false agreement. Because something will happen to immediately cast doubt over this false agreement, right? That's what launches your story.
Once you have your false agreement sketched out (spend 15-20 minutes freewriting on what it could be), your next step is to chart how that agreement will get busted up.
In all stories, there are small and large epiphanies where the character gradually realizes the agreement may not be all it's cracked up to be. Maybe a hint of that is early in the story, within the first third. It can be a small epiphany, or turning point.
But the character often perseveres and tries to keep the false agreement going. Then there's a bigger event that cracks it even more: often, at this point, the character decides not to take this #%$$ anymore and reinvents themselves or gets new help or new clues. This might happen midway through the story.
There's is often a revision of the false agreement, a new false agreement, if you will, that is closer to the truth but not quite it. (Why? Because you still have half the story to get through, and false agreements create the conflict that drives the character. So you don't want to get rid of the false agreement entirely, not yet.)
Usually, near the end of the story, the smaller epiphanies result in a major one. At this point, the character sees truth.
They become different, fundamentally. And they make changes that really show how far they have come since the start of the story.