This is by far the best description of ‘agency’ that I’ve ever read:
It is characters who create problems, who escalate the problems, and who inevitably complicate and then fix the problems. Characters want things, and in pursuit of those things, they fuck up and fail and then succeed as heroes. ~ via Chuck Wendig
Everyone always says you need to ‘give your characters agency’, or ‘the characters should drive the plot’, but in concrete terms those descriptions of agency have always been pretty meaningless to me.
I’ve struggled with it in my past novels, because the characters were too busy running from or reacting to what was happening around them to drive the external plot. I was going with the ‘chase character up a tree then throw rocks at them’ model of plotting, which left something missing.
It’s simple now that I think about it this way:
Have your characters create their own problems and suffer the consequences for good or ill. Let them fail once in a while, let them make bad choices, then fix them. Bonus points for snowballing problems.
Cue light bulb.
Character agency, decoded.
*YMMV, but it works as a mental model for me.