Drawing on their own life experience, they've written this scene or that character down exactly as it was in real life, just adapted so it's now set in the old West, or Space Station 29, or whatever. They forget that they are writing fiction, not memoir or autobiography. Whatever meaning that scene had in their own life, however great a resource for generating ideas and engaging their senses, such experiences cannot be incorporated too literally. We get to change things in fiction. Have to, really, if we want it to make sense in the context of the new story that's being written. It's not about capturing reality, it's about understanding what meaning the scene could have for the reader.
Or, sometimes the scene is entirely fictional, but that's the way the author pictured it doing their first draft and so that's the way it has to be. This one usually manifests as 'bloat': the scene may be off message or completely unnecessary, but cutting it strikes the author as a betrayal of the vision. That's okay for the first draft, and maybe even the second, but by the third draft it's not about your needs, it's about what the story needs. As one author put it, the first draft is 10% the book, and 90% the author (i.e., about the author's ego), draft five is 50% author and 50% the book, and it takes to draft 10 before it's 100% about the book. If the editor says a scene has to go for the story to remain on message or to skip over the boring bits, listen to the editor.
Of course, one can go too far the other direction, fictionalizing what actually happened so that it becomes not just unrealistic but outright self-indulgent. Sometimes, recalling what that bastard said to you at that party that time, and editing that scene so the "what I should have said" reply you thought of two days later becomes instantaneous clever repartee in the book, works. Maybe that traumatic experience can be rewritten in your novel to include a suitable revenge scene that provides catharsis for readers with similar traumas. But, um, you can see how constantly rewriting life to be perfect can easily go off the rails so that as the hero of your own story, the protagonist is too clever, too powerful, too lucky.
That's why one has editors. If the editor says, "I love your protagonist's repartee", you're good. But if they say, "Really?" then maybe go back to having the hero embarrassed, deflated, and beating a hasty retreat—the way it happened.