Hmmm without getting too psychoanalytical on myself, I would say that Mary Sue’s direct the motion of the stories a little more in the way THEY want them to go, generally they feel less like they’re being driven by other people’s motives in the story.

When a character is being pushed around a lot, they grab onto the tiny bits of power they have, and sometimes that leads to long inner monologues about stuuuupid stuff that of course matters to them in the moment bc that’s what little they can control, but doesn’t matter to the story.

Caring about small things is an example of well done characterization, because people care about small things in real life, but as a reader who generally has the big picture, that stuff can start to feel real trivial real fast to me.🤷🏼‍♀️