Agency sounds like guys in suits with dark glasses stuffing you in the back of a van, but it's kind of the opposite of that.
If they're not pursuing their goals, or not affecting the plot, they lack agency.
The plot is all about trying to Stop The Villain From Doing Bad Things, rather than what the characters might want.
Or we're just following a prophecy like it was a cake recipe.
It feels natural to make the story something that happens TO the characters.
Because there are problems that come with lack of agency.
Moments of choice are vital to defining character. But if I’m too busy dodging assassins and following my prophecy cake recipe to the letter, I’m not making any important decisions.
If our hero is just reacting to a series of events—no matter how exciting—the story falls flat between them.
The reader has nothing to draw them onward.
Ask yourself these questions, both in general and on a scene-by-scene level:
We need to see them doing stuff to try to get what they want, and not just sitting on their hands hoping someone will hand it to them, or letting some mentor figure drag them along the path to victory.
This doesn’t need to be the effect the character intends. Their plans can go horribly wrong. Their actions could even make things worse.
But things should be different because they tried.
Not only can you fix this, but fixing it often will take your book to the next level.
Well, maybe instead of getting randomly jumped by kidnappers, they get captured when they’re in the midst of sneaking into the bad guy's lair.
It's hard to give examples without being spoilery, but for instance, in THE DEFIANT HEIR, Amalia makes a big decision at a party, around the end of Chapter 4. It affects the whole book.
Luckily, I realized this robbed Amalia of agency, and asked myself "What if she made this choice HERSELF? What if it was HER IDEA?"
And the book was SO MUCH BETTER for it.
But overall, it’s important to make sure our main characters are propelling the plot forward, not being dragged limply through it.
But they need to keep trying.
If Sisyphus takes a nap, the tension is gone, and we put down the story.