When one thinks about it, writing a book is a lot like being like Coleridge's Ancient Mariner. The reader is the wedding guest, a guy who's got his mind on much more fun things than to listen to your story, and who's very resistant when you collar him and demand that he pay attention.
Your task as a writer, your curse if you will, is to grab the reader and hold him or her, if not literally, then with an arresting opening ("There was a ship") and then not let go. As the poem attests, you can take the reader far afield from their usual experiences, but you've also got to go deep into the story and character. You've got to make them care about your protagonists and feel the protagonists' struggle is theirs. The protagonist or the message may be complicated or unsympathetic. It may be literally incredible or fanciful. But if you take the reader on the journey with you, then she or he'll be willing to accept whatever you want to tell them.
On that journey, you have to hold their trust in the story. You can kill the lead character, you can weigh the protagonist down with guilt and horror, you can speak of the unspeakable and break any number of rules and leave the reader feeling storm-tossed or becalmed. But you cannot betray their trust in the story-telling: you keep looking them in the eye and say, "Bear with me. The journey is not over yet, but we will eventually get home."
The result, if you do it right? Your reader will be a "sadder and a wiser" individual. That's not to say your work has to be sad or wise; it doesn't have to be as phantasmagoric or allegorical as the Rime. But the reader has got to feel that deepening, that sense of having been taken some place else, that comes from being told a transporting story. You know the feeling: the sadness and satisfaction you get when you feel the story coming to an end, and that the border-crossing between the land of your imagination and the mundane world beyond is in sight. And you have to do it each time, with every wedding guest. That is your curse as the writer: to travel the world for the rest of your life trying to get people's attention, grabbing one in three, or one in three hundred, and attempting to stop them from entering their much more attractive entertainments to hear your own. There was a ship.