We've all read books in which the good guy versus the bad guy, and a few other things happen in between. I want to suggest that those kinds of plots are basically the protagonist's motivations pitted against those of the antagonist. And this is just one reason it is important is to know your characters - to know what they want, what they would do in a particular situation, and why they would do it. The action in a story is, of course, secondary to the "why". The "why" is all-consuming.
And the reader needs to know.
Within the first few scenes of your book, take a moment to make sure that you've shown some of your main characters' motivations and desires. These motivations will lead to the actions that should drive the plot. After all, the author shouldn't be the one that holds the happenings of the story with an ironclad fist. The story should happen because the people happen. That's how it goes in real life. That's how to make a story credible. That's how to make your readers care about what you write.
For instance, the Forsyte Saga (an incredibly long read, but well worth it) is an example of a monumental and influential work that is character-driven. Irene is seeking freedom, and Soames wants to keep her under his control because he is a "man of property". It is the desires of these two that determine so much of the series.
It's not enough to show people entering the army and undergoing gruelling training for no reason at all. It's not good enough to show a king waging an expensive war, without ever explaining why he is fighting. It's poor writing to have a villain who is a killing machine, but has no compelling motivations for being so. Something must have happened to him - he must believe something, desire something - that has caused him to justify his actions.
Many publishers today are far more interested in a story that is character-driven rather than plot-driven. This is evinced in the kind of rejections that big publishing houses send out today. And I should know because I've had a few of these.
The question is: do you know? Do you know what distinguishes a good book from others in the eyes of readers and publishers? And are you willing to do what's necessary to bring your book to the next level?