Full-Circle Plotting in Books
When does the magic happen?
In thrillers, the full-circle moment when something tiny mentioned in the first act becomes the catalyst for solving the case by the end can be a truly satisfactory experience. Personally, I prefer when the detail is tied to the antagonist’s motivations for the crime, but a clue that the protagonist finally interprets correctly really elevates the novel, too.
While the twists make the book exciting, it’s important to keep the scope of your story contained. Have you ever read a book where the bad guy was a brand new character or someone barely mentioned in the book? Or perhaps more and more events were happening, but they weren’t connected to each other in a cause/consequences way? It can feel overwhelming and hard to follow. Designing your events to be fully dependant on each other helps the readers feel invested. Bianca Marais (the host of my favorite TSNOTYAW podcast) calls this the domino effect.
The protagonists' actions are in a constant relationship with their circumstances. Everything they do should impact the plot in a meaningful way. When a new obstacle presents itself, it shouldn’t come out of the blue, but should be a complication created by the antagonist in response to all the progress the protagonist has made.
Whether you’re a pantser or a plotter, the connective tissue of the story should emerge during the writing process—an aha moment that comes from a throw-away line or hours of brainstorming.
In general, it’s nice to have things tied with a neat bow so the reader is satisfied by the end of the book. However, I would caution against trying to make everything connected to everything. It can mess with plausibility, especially, if you’ve already answered the major questions.

Ohhh... I love these innocuous looking loaded Chekov's guns, sprinkled all over a story. I love especially, when later down the line, they go bang and this innocuous event/object, suddenly has a deeper implication in hindsight.
And as you said the trick is to do it organically. Make the reader go — "Ahhaaa... Why didn't I see this all along? And now that I see it, it makes complete sense."
Having obstacles prop out as a reaction to the protagonist's actions, rather than our of the blue (for plot convience), is such a good point.
And the point about — 'keeping the scope of the story contained' is so legit!
I love these short, but content-rich advice posts. Thank you sharing!