Books that start slow and stay slow are fine for intellectual improvement. If we’re writing to entertain, we need to be more aware of the speed of our story.
During the first 25%, the Setup, the pace is often slower, because we’re introducing our characters, setting the stage for the hero so when we get to the First Plot Point we’re invested and engaged; we care about the stakes.
But when we hit the Second Plot Point, we’d better be set up for a chase scene. The final 25% of the book, your Climax, should be unputdownable. Not only is it right for most stories, it’s what your reader will remember when they finish.
Plenty of tips and tricks out there in the ether about creating and adjusting appropriate pacing. Getting it right, matching your genre and the place you are in your story, is like using exactly the right spices in a dish: miss by a little, maybe no one notices.
Nail it, and you’ve got a hit.