So let's say you are writing a story. In order to give the story the flavor you want, you need to use a particular body of knowledge. Either this is a body of knowledge that you've created yourself - say, through extensive worldbuilding about climate, geography, etc. - or a body of knowledge that can be accessed through research, such as the history of English language and culture, or that of Japan.
With a created world, this problem is almost more straightforward. You can assume that readers unfamiliar with your world will simply not know anything at all. There's a great solution for this sort of thing, even if you are so steeped in your own world knowledge that you can't judge how much is making it onto the page. You find a "naive reader," i.e. someone who is totally unfamiliar with your world, and let them loose on the story. They'll be able to tell you where they stumble, where they are confused, etc. They will be a perfect model of your target audience.
With the real world, it's much trickier, because you can't anticipate how much information your reader will have. Some of your readers will share this information. Some will know nothing about it. Some will be experts And you, believe it or not, are trapped in the middle.
I encountered this strange difficulty with a story I wrote, using a Japanese setting. Some people have loved hearing the story. Some have felt totally lost, and appear to have problems because they don't know enough about Japan or Japanese mythology. Some have felt like the story was too transparent, because they already know so much about Japan and Japanese mythology.
It's enough to make one throw up one's hands and go, "Argh!"
There's another issue here as well, and that is the issue of trusting the reader. Some readers will be okay with not knowing quite what is going on, not quite understanding everything; others will not. This actually means that the number of people who have serious trouble with the story will be smaller (fortunately) but the underlying problem remains.
My best suggestions are as follows:
1. Get a wide range of feedback. Take this feedback seriously.
2. Provide subtle contextual scaffolding.
What I mean by subtle contextual scaffolding is that you want to give hints that will eliminate confusion without actually giving too much information and making the informed people scream. I had one reader be confused when I included a direct translation of a Japanese idiomatic expression, "the nail that sticks up gets hammered down." Now of course, I can't actually explain the idiom in context - but what I can do is support it in other ways that will be more relevant to the main character and to the conflict we're dealing with. If he doesn't just think this in an unquestioned way, but thinks of someone who always says it, for example, it will make more sense, and people who already know the expression will gain character and setting insights so that the information provided won't be entirely superfluous. This is the perfect kind of place to make sure that whatever you include serves more than one narrative purpose at once - advancing plot, deepening character, reflecting and deepening setting, etc. People will be bothered by explanations that are only explanations. But they might be more interested if the explanation they already know gives them an insight into another area of the story that they know nothing about.
It's something to keep your eye out for.