What's lost when you're past learning
Once you've learned a language to a high level of fluency, you can't help but understand spoken phrases and written signs.
Imagine a piece of paper in front of your view with a word from your native language. You won't be able to keep yourself from instantly reading it and bringing to mind its possible meanings.
Just replacing that piece of paper with another with a word of an unfamiliar language (or unfamiliar script) is enough to break this second-nature understanding and render the contained information completely out of reach.
And yet, that second piece of paper can be as naturally understandable to millions of people if it's their own native language.
What's interesting to me is how, after I learned engineering and the sciences as a framework of understanding the world and its phenomena, and having practised it for almost a decade, I can grow completely oblivious and plainly blind to other's own lived experiences which don't share the same assumptions.
I don't mean to imply there's a more correct way or superior way of understanding and viewing the world, and there's not even a need to establish that for my argument that follows.
In the same way that your own native language can be second-nature to yourself -- and you can't understand (beyond an intellectual level) how others make sense of foreign languages -- your own way of understanding and making sense of the world can be so ingrained in your own thought process that you lose the ability of comprehending how others can arrive at different conclusions.
Let's dive into another example. As a kid, you had to be taught on how to read an analog watch. After you're taught and practice doing that for some years, you can just at a glance tell what time it is.
Yet, to teach someone else, you can't tell them “just look at it!”.
You have to break down what each of the numbers in the dial means, in what direction the hands move, how the “hours” hand advancing one subdivision indicates the passage of one hour, but the “minutes” hand completing that same distance indicates 15 minutes instead, and so on.
Only when you have to explain it you can realise how much assumed knowledge there is in your own thought process.
For successful communication to occur, you have not just to break down the concepts and terminology, but also understand the person you're hoping to reach and meet them most of the way they are.