And this is exactly the reason why communication is so difficult. What happens when the Speaker misjudges the amount of information that the Addressee has? Yep, miscommunication. And it happens all the time.
Now, let's complicate things even more. Suppose what we have is only half the conversation. Suppose you come across a letter from your grandfather to your grandmother in a trunk. How much of what's going on can you follow? I suspect quite a bit—assuming you knew them both.
OK, let's complicate it even more. Suppose the letter was written in Swedish (my grandfather was Swedish). How much will you understand? Even if you do learn Swedish, it will likely be a more archaic version that they are using. Word meanings change over time.
OK, it gets even better. Suppose that we have a letter, written in an ancient language called Greek, written to a group of people living in an ancient city called Corinth...what are the chances that we are going to understand what's going on?
And you wonder why we disagree? You wonder why there are so many commentaries and translations? It's a marvel we agree on anything!