I've mentioned that my first job out of college was with a children's publisher, and it was not an easy transition. One of the major shifts that had to happen in my mind-set was the question, Who carries the burden of understanding?
When I was an undergraduate, working toward my fancy honors degree in English literature, I knew the answer to that question: It was the reader's job to understand what the writer meant. I was quite dogmatic about it. Don't know what that word means? That's what a dictionary's for, idiot! Didn't understand the book the first time you read it? Read it again!
I got very frustrated with my classmates, who for the most part were not English majors. They read for entertainment--they didn't want to have to use the dictionary or read something three times to understand it. I had nothing but contempt for them: They were lazy bums.
Fast forward one year, and there I was, writing for kids. Wow. Yeah, kids. I read a lot as a kid, and it's not like I was going to good schools, so I could definitely relate to the fact that here was an audience that (through no fault of their own) knew absolutely nothing but that wasn't stupid.
And that's when I realized where the burden actually lay: It lay on the writer. I had to make my writing very clear. I could not throw out some half-coherent mumbo-jumbo and say, "Well, stupid, figure it out!!!" to an 8-year-old at a school where the teachers are all high and the students are all reading two levels below their grade.
It also meant that I needed to write like a person who was very literal-minded, because that's what kids are. (I remember being horrified by a Soup book in which the kids throw rocks at a guy's house and he runs out "with blood in his eye." I thought they had put his eye out with a rock, and I was totally shocked that neither the kids nor their parents felt particularly bad about it.) That's why I worry about little things, like where I put the word "only" in a sentence--I don't take for granted that the reader can figure out what I mean if my words are in the wrong place.
This concept that the burden of communication lies on the writer, not the reader, is a very controversial one outside professional writing circles. (Inside professional writing circles, it is a given, because if you cut yourself off from the majority of readers, your stuff will never sell.)
One group that does not accept this notion is academic writers. If you want to get promoted in academia, you have to make everyone feel like you are smart and they are stupid (or perhaps they can smugly feel like they are in the same elite circle as you). The result is that a premium is put on obtuse writing. As a result, nobody reads academic writing unless they have to. People read it because they are forced to, by their professors or because of their line of work.
Would-be writers often have gone to college and been told, Hey, you reader, you must work very hard to understand these books, otherwise you're a failure. And they think they can turn around and do this to their readers. But guess what? Readers don't have to read you. You're not in that position where you can assign your book to a reader, and they have to buy it and read it and regurgitate it on an exam, or you give them an F. You don't have that kind of power (which is probably a good thing).
Another group that struggles with this idea is what you might call the talented amateurs. They write for people they know, who love them. That's great--I do that too. When I write my loved ones I use shorthand and don't worry so much about grammar and put the word "only" in wherever, confident that the person reading it can and will do the work to understand what I'm saying. And they do--it works great!
But readers are another matter entirely. Readers don't love you--they don't even know you. Even if they say they love you, they mean that they love your writing. Because readers do not love you on a personal level, they are not going to do the work to compensate for your shortcomings. They'll just put your book down and not pick it up again.
Now, I will agree that poetic language often isn't that clear on a literal level (although it can be). But I'll argue that the good stuff makes plenty of sense on a thematic and emotional level.
And people use the, "It's poetic!" argument to justify murky writing about subjects that really shouldn't be unclear. If you're describing how a building that is about to be robbed is laid out, or you're trying to communicate some background information that will be important later, that kind of thing needs to crystal clear. You're not talking about some ineffable emotional state or something like that. You're just delivering information the reader needs to understand your story. The harder you make it to understand this information, the harder it is for the reader to become emotionally engaged in your story. And a reader who isn't emotionally engaged is a reader who will cut you no slack at all.