This page might get large revisions to make the ideas expressed more clear. This makes sense given that it is about how nothing can be expressed perfectly clearly.
Information goes through hundreds of levels of abstraction before we can say that we understand it, regardless of how it is communicated to us. It is impossible to say for a fact that any information we receive is as it was in its original form, and that our understanding is complete. In lots of subtle ways, the information has changed, and we will never be able to say how.
The most obvious thing to elaborate on is language. Even if two people speak the same language, their understanding of the language is not the same. Incompatibility of language is not just between those who know complicated academic words and those who do not, or those who know special regional slang and those who do not, but often runs much deeper. Even the most simple words can vary in meaning slightly from person to person. People set different limits for what is 'simple', for an easy example from this very paragraph. One can elaborate on what they mean by 'simple' and appear to increase understanding somewhat, but without any certainty that full understanding is actually achieved. Any elaboration is going to be based on adding more words that could also easily be misunderstood, and is often made up in the spur of the moment as people do not often think about how people might perceive simple (oops) words differently.
How one defines many of the words they know is affected by how one define themselves. A person who thinks of themselves as left wing will have a different view of words like 'democracy' or 'free' from a person who calls themselves right wing. A left wing person may think that hierarchies prevent democracy and prevent freedom while a right wing person may see hierarchies as a consequence of democracy and of freedom.
Americans descended from Ireland like to view themselves as Irish and have their own conceptions of what 'Irishnesses' is. But in Ireland, the views will probably be very different. Some might feel you need to be born in Ireland to be Irish, be naturalized as a citizen to be Irish, or to have certain values that they think of as having a quality of 'Irishness'. In any of those cases, there are more questions that can be asked that break people up further.
Every word or phrase also might for someone have an emotional response attached to it that others won't share. These responses develop over time and are never the same. Emotions are more complex than words like 'happy' and 'sad' are taken to be, as they are a mix of different sensations at different levels. We cannot measure these sensations except through abstract guesswork. We cannot fully understand a positive or negative emotion someone else associates with a word, or how this will alter their perception of what you are saying. Lots of arguments begin this way very innocently.
The word 'queer' can be used as an especially easy example to the last point as it is very controversial. It is an insult that has been reclaimed in some places and persists in others. Even if you are around a group who use the word positively to describe each other, you may feel uncomfortable with it if you have had bad experiences with people using the word negatively in the past. You could become very fond of the people who are now around you, and this could cause your feelings to become quite complicated to describe.
There are many more levels of abstraction. Language is not even the beginning. We are limited more than anything of by our senses, not able to measure a lot of things going on around us. We cannot see infrared light, for example. We are then limited by our brains, and how they make sense of the information we receive. We cannot say that one person's blue is the same as another person's blue, for another example.
We look at something. Our eyes only capture the light patterns expressed by the material world. Our eyes can only process this information with the help of the brain. The brain can only make educated guesses about the world based on previous experiences. The brain works differently in individuals according to their individual biology and chemical levels. The brain puts information within the framework of a human language. The information becomes a memory that changes as we forget or make new assumptions. The memory goes from short to long term. We tell someone else about this. The memory moves back to short term. The memory is translated into new words. The words are altered for the audience. The words are expressed verbally in a particular voice. The words are heard at a particular volume, through other noise. The accent is deciphered in the brain. The meaning of the words is judged according to personal understanding. These are all layers of abstraction, and there are surely many more that are not listed here.
Many powerful hallucinogens exist which can completely warp our perception of reality in a very short space of time, even in small doses. The sounds around us change. The sights that we see change. The language in our heads change. Every aspect of reality can melt away into something else. It reminds us that the brain has a great power to misrepresent any communication from the physical world, and that the brain is extremely sensitive to its biological conditions.
The way that we see ourselves is particularly hard to communicate. To us, we are many years of memories, and of established thought processes and specific tastes. To the rest of the world, we are a collection of poorly translated sense messages and biases. Even the most in-love of lovers can view each other in ways that are entirely inconsistent with inner views. Having a false perception of another person is not even just 'normal', but the only way we can have any perception of another person at all. The image we project may be more important than the way we view ourselves. If a person acts badly, that is not negated by the fact that they are secretly insecure and love kittens. However, as individuals we generally desire to be understood, and from that perspective it is still sad that full communication is impossible.
On the other hand, perhaps it gives us something to strive for. When we recognize that nothing can be communicated perfectly, and we understand that means our understanding of each other can never be perfect, it is harder to become complacent in our learning. Even after 50+ years of marriage, there will be things a person does not know or understand about their spouse, and this is encouragement for continuing to learn about them and to grow forever closer.
When perfect communication is impossible to be sure of, one might be tempted to say that perfect knowledge is also impossible. Again, we could try to find positivity in this rather than despair. The world is vast, varied, and mysterious. There will always be ways in which we can keep learning and changing. As long as we continue existing, we can be surprised. This can make living interesting.
And finally, there a lot more to 'communication' than just perfect communication. There is a lot more to 'knowledge' than just perfect knowledge too. This piece is just about encouraging a certain mindset. We have to remember not just that nobody is perfect, but that nobody is even close to being perfect, and if they were then nobody would even know. We have to remember that words can mean different things to different people and at least do our best to try and understand where others are coming from. We have to remember that even our basic senses cannot be trusted completely. Everything is open to doubt.