An author of narrative fiction (I’m aware this is a horribly broad brush I’m drawing with) is faced with the decision of how to manage the reader’s expectations towards the heady pull of the plot. As in, at a first approach, the reader wants some kind of build and release - but if that’s all you get every time, it’d be kind of boring.
The advantage, narratively speaking, to playing with ideas of agency, is that it allows You (the author) to subvert the expectations of the reader without disappointing them. That is, the plot may still move through its nice arc of tension, but your character may end up unsatisfied for (perhaps even inconsistently held) reasons of their own, which leave an interesting aftertaste in the mouth of the reader. Made explicit, this author-reader dynamic gets you Calvino’s If on a Winter’s Night a Traveller, where the expectations of the reader themselves form the narrative tension. The Reader (the character in the text) has a choice each time about whether to pursue the narrative further, and the Reader (you) does too. Calvino is flirting with you: it’s a game and it’s silly and you can be in on the joke with him, and so critically action still follows from motivation (you want to keep reading each missing book). Something like Molloy is a more hostile version of the same challenges to conventional narrative. The reader is asked to persist regardless of the lack of gratification or tension; in some way our motivation and our behaviour become divorced.
There’s some nice side paths to venture down here - like, how does a Reader differ from a Listener ( Molloy versus Waiting for Godot, or the Iliad to say, Dante’s Inferno)? But what I’m most interested in is when and how did characters start to see themselves as separate from their own motivations? Has this spread into our consciousness via narrative (because it makes for characters more interesting than your average Christie criminal - when wills are less clear, if you’ll pardon the pun) or to narrative via society? I’d argue it’s pretty clearly not an ancient conception of self - the heroes of the Iliad, for instance, hold their agency tightly, except when it’s tempered by immortal intervention. Achilles is the most tortured, but even he is clearly acting in accordance with his own desires, at least of that moment. His fate is manipulated, sure, but from without, rather than within. Perhaps it’s the threat, always present in the Iliad, to make human beings into things, which is hardly moderated by, say, the thing having thought that there were multiple forces within itself, y’know, subagents and stuff.
There’s obviously more literature out there than I can take in on selfhood and agency through the ages, but the point is that this stuff matters, right? The way we think about ourselves really does impact what we attempt and how we go about it. Maybe not as extreme as causing all of human progress but enough to change the kind of life we lead.