I've become more aware of how writers write as I hone my own writing, and one thing I notice that we (yes, me too) do is put too much of ourselves into a work. As a teacher, I want to teach, so I have to guard against putting lessons on Scottish history into the middle of an otherwise swiftly-moving story.
Now that I've admitted my own fault, I notice that it happens to other writers as well, some much more famous than I. Sometimes it's just the irresistible urge to put in a factoid that the writer found too cool to leave out, and that's not so bad. But when the reader must endure several pages of the writer's opinion of modern psychiatry, industrial practices that pollute, or governmental indifference to the lower class, I begin to wonder, "Where was the editor in all this?"
The book I'm reading now, by a slightly famous author, keeps stopping to give the reader lessons: temperatures in the Gulf of Mexico, stages of grief, laboratory procedures. The author sometime tries to camouflage them by making them dialogue, but no real-life person who lectured his friends at such length on any topic would be invited to their clambakes a second time.
I remember reading Sinclair's "The Jungle" as a young person and being disappointed in the ending, which wandered away from the characters I'd come to care so deeply for and descended into a socialist diatribe.
Some authors can do it. We don't mind a bit, in fact we love it, when they teach us what they learned in research. It's done quickly and cleverly in most cases, woven into the fabric of the story so it doesn't appear as a black and white patch atop the color, and they have a sense of how much to tell, how much we want to know before we return to the characters' lives.
As writers of fiction, we should keep in mind that we aren't teaching the reader. We can only show what exists in the world we create and let the reader draw her own conclusions about how that applies to reality.