I was a bookworm kid, and I distinctly remember a certain phenomenon occurring with a subset of the books I devoured as a child.
I would start to lose interest in the book around the halfway point. Because that was when "the plot" started to pick up. And even though that was supposedly what we were reading the book to enjoy . . . it always seemed to be when I started to tune out.
So why was that? Was the plot boring? Probably not. Was I just not the right audience? I doubt it. Did I have a terrible attention span? Definitely not.
The reason I'd start to feel disinterested right when the momentum kicked it up a notch was that this was when the author switched from drawing us into the "who" of the story and started focusing on the "what." And for me to care about what was happening, I needed to stay connected to the characters throughout the action. You can't just get me attached to the people at the beginning and then abandon that sensitive, personal narration in favor of plot points. I stop caring about what happens in your book as soon as the focus shifts from "PEOPLE (doing things, with things happening)" to "THINGS HAPPENING (to people)."
Now as an adult, it surprises me how often books do this. Maybe it's because stories typically start with characters minding their own business introducing us to their regular life, before The Plot begins and turns everything on its ear. We see the character in their natural environment, and when the author's good at this, we feel more comfortable with who we're reading about as we learn what's important to them, what their relationships are, and what their motivation is. There's a little leisure there; we patiently soak up the character's present situation, looking forward to seeing how this person will deal with whatever's in store for them.
But then it seems like the pressures of "telling a fast-paced story" pull us out of the moment and wrench us out of the characters' minds in the interest of keeping the hearts pounding and the pages turning. I think that even in a plot-oriented story we still need to see characters with agency letting us understand why they're doing things, what they're feeling when things happen to them, and how they're staying mentally present as they build toward the climax of the book. The author sets a scene at the beginning, but then takes it for granted that we, the readers, will maintain it. I don't like when I get that familiar sinking feeling when "the plot" starts and I realize this author is one of THOSE storytellers whose characters become a weird collective chess game instead of maintaining their individuality as the pieces.
Authors, do me a huge favor and don't let your plot get in the way. Stay in your characters' heads and keep the forward motion connected to their decisions and reactions. Don't let us start seeing the scenes as filled-in points on your outline. This isn't high school math class where I want to see your work.
Authors I've known to remain bravely character-oriented in the face of Plot:
K.A. Applegate, Ann Brashares, Charlotte Brontë, Octavia E. Butler, Stephen Chbosky, Suzanne Collins, Diane Duane, Katherine Dunn, Jeffrey Eugenides, Shannon Hale, Stephen King, Wally Lamb, Eloise McGraw, Jaclyn Moriarty, Julie Anne Peters, Spider Robinson, Louis Sachar, Jerry Spinelli, and Joan D. Vinge.