Terry Nation, the creator of the Daleks, Blake’s 7 and The Survivors, was interviewed yonks ago by the Radio Times. As I recall, he said something about wanting his work to be educational, but had misgivings about using that word. The interviewer suggesting ‘intellectually stimulating’ and Terry wished he’d thought of that.
I wish he’d stuck to ‘educational’; that’s ‘learning something’, not sitting bored for hours and then having homework.
If stories are about communicating the theme (Lesson#1: stories must be about something), then the audience must learn that lesson. They may know it already, but essentially a story must present the ignorance, give the lesson and finally present the wisdom. Now no-one wants to be lectured, so a story must present its material dramatically. Usually the audience’s representative is the protagonist, and so it is the protagonist who learns the lesson.
(There is an irritating exception: a story where the protagonist doesn’t learn anything. Take a theme like: “what we learn from history is that no-one learns from history.” So, the ignorance is presented, the lesson given, but the student protagonist is none the wiser. Alternatively the hero of the piece is unchanged, they are the lone gunman who rides into town and leaves at the end exactly the same. However, even with these a ‘tagonist’ of some variety learns something, it may be the antagonist, the deuteragonist or simply the audience-tagonist. It may be the town that realises, after burying all those killed in the shoot out at the end, that it shouldn’t let lone gunman in again. I’m going to ignore this exception, it’s one for discussion certainly because it is possible to write stories like this BUT most stories without the protagonist learning aren’t actually saying anything. They’ve been written by someone who believes that “rules are made to be broken” and “you don’t have to tie up all the loose ends”; these people don’t actually know the rules and deliberately add threads to dangle to wave around and… I’m ranting, so I’ll stop.)
So, the protagonist (or whoever) must learn a lesson as an example to us all; if nothing else, what the story is about. Even if, taking the history example, above, no-one learns anything, then that in itself is a lesson.
Therefore, a character (main, hero, reader, audience…) must learn something.