I started a conversation in r/screenwriting about how to sum up a complex story/setting into something like a logline, and one poster started talking about identifying my "central theme", and then things just got a little confusing for me from there. I'd like some help in sorting it out.
The gist of my confusion is this: when I search for common film or literary themes, I find lots of sources listing single verbs or nouns which describe things that humans do or experience. "Love". "Death". Loss of Innoncence". "Betrayal". Etc. But this poster was trying to help me understand how a "true theme" is really more like a statement or a message. He provided an example in Schindler's List: "you should stand up to evil instead of being neutral". I pointed out this was just a moral opinion, and possibly not the only one that could be gleaned. He then said it doesn't have to be moral, and provided another in Groundhog Day: "you should be decent and genuine instead of being stuck in a selfish rut". I pointed out that this was still just a moral lesson, at which point we kind of started talking in circles and didn't make much progress.
I want to better understand the kind of theme that poster talking about, and even better, identify what the central theme is in my own already established story. He gave me some direction as far as saying "if you find the motivations of your protagonist, especially towards the end of the story, this will probably be your theme." But I'm still having trouble taking it from the three motivations that my protag clearly has for entering the final conflict, and summing it up as one central thing, which, according to this poster, is ultimately the "why" of why the audience should care. This makes matters worse for me; I can't connect with this idea because for me it's all about the characters, and frankly dissecting a story for the underlying message has always been something I find tedious and not actually meaningful or interesting at all. By which I mean a single central theme is almost never going to be the reason I care.
I realized he may have been talking in terms of screenwriting in particular, so I thought maybe taking this conversation to a more general writing forum might help me figure this out. This story has been envisioned as both a novel and a screenplay (or even a graphic novel or animated mini-series), so it's not set in stone which medium should be used (that might be another question I need help with).
So first I'd like some input on understanding this idea in general. Specifically I'd like to hear an example of a theme/message that is 100% not a wannabe moral lesson or even inspirational in any way. For instance, how might we frame the theme of a story where the bad guys win? Or something like a horror story? I'd like to hear some examples of themes that say truths about the dark side of existence/human nature rather than the uplifting/moral lesson side.
Once that's accomplished I can maybe go into some specifics of my protag arcs, or even link to a short outline of those arcs, if anyone is willing, to see if we can't maybe pin down the one for my story. But first I'd like to understand the concept better in general so that maybe I can do it better on my own. Internet searching has not been helpful so far and again just leads me to single verb or noun words that are nevertheless called "themes".
Feel free to link to a specific text/discussion where you feel this concept is already expertly addressed.
Thanks in advance for any direction anyone can provide.