When I'm simply reading, I read with the consuming desire to know what happens to the characters and what it all means. This desire is undiminished by the knowledge that the people and events I'm reading about don't actually exist. Indeed, there's a sense in which I think it is stronger, knowing that I'm reading fiction, in that I have a certain faith when reading a novel that it will all mean something in the end. (If I get to the end and find that it doesn't, I'm usually angry.) The fiction writer filters through and chooses what events to portray based on the meaningful version of the world being portrayed. And thus, if the writer is good, every thing which is described in the novel has a reason for being there. Not just "that's what happened next" but an actual reason. A reason why we need to know about this.
This has been striking me in a paralyzing kind of way at the moment, because I've been reading a lot of diaries and memoirs. A diary is also a filtered version of reality. The diarist writes down what is important to her that happened that day. But a diary doesn't tend to have an overarching story.
Right now I'm reading Florence Farmborough's With the armies of the tsar: A nurse at the Russian front, 1914-18, the diary of an English woman who was working as a governess in Russia when the Great War broke out and spent the war working as a nurse in a front line field hospital, before having to escape back to England after the Russian Revolution transitioned into a civil war. It's fascinating reading. But one of the things that has had me thinking a lot is: How would this be different if it were a novel? Here's another page long anecdote I which Florence deals with a badly injured soldier who dies of wounds while she nurses him. It's different from the scores of other times Florence writes about dealing with such a situation, but in another sense it's "yet another time Florence helps a dying soldier". In a novel, would you skip a lot of the medical detail and every-day suffering because it would be repetitive? And yet, what's what Florence is dealing with every day. The incidents she deals with may be repetitive in a certain sense, but it's the sheer repetition of difficult situations which gradually changes her over the course of the war.
Sometimes it seems like very dramatic event is "part of the story". Other times it seems that if this was a novel you would cut out most of the events but come up with a clear idea of how Florence's essential changes progress because of the few events you portrayed.
Maybe both are acceptable ways of writing a novel if done right. There's a sense in which, reading a diary first published forty years ago about events which took place a hundred years ago, I'm reading it as fiction. I don't know they people involved any more than I know fictional characters. And yet, it seems to me that there must be some way in which I, as a reader, interact with the book differently than I would with a novel which relayed the same events. I make certain allowances or give it leeway because I know that the author didn't know what "the story" was as she wrote it. Her author's filter was at the day level, not the overall story level. So what keeps me reading, knowing this is a journal, is probably different from what would keep me reading if it were a novel.
As a reader it's easy to pass over the question of "should this incident have been included", but since I'm reading a diary as if it were a novel (and trying to do research related to writing a novel) the question seems to come to the fore.