A rule referred to as Zipf’s Law is the foundation of all communication. Anything that corresponds to anything follows it. Knowing it can allow someone to mark something’s significance. It’s how archaeologists can determine lost truths with absolutely nothing to go by. Once the basics are understood, then each thing that imperfectly corresponds to something else is compared with other things with the same meaning. You could compare this to triangulation. From there, the rest can be achieved.

A̵̧̲̞̭͖̟͛̑͋͌̓̈́̕͝͝l̴̢̢̡͈̙̬̝͇̙̼͎̂̉͑̓̄͌̒̀̇̐̀̔̚͜͝ͅļ̷̡̟͎̱̗͉̟̬̖̟͖̦̏̄͋̒͐̏͝ ̵̯͇͎̼̪̳̭̞̫̹͗̒̊̄̽͛̏̈́̓͘͝͝͝͝͡c̸̭̠͔̤̣͚̭͌̈̂̇o̵͙͚̜͉̞̰̎͐n̷̡̘̘̻̦͋͆v̴̡̢̙̱̟̦̞͉̣̟̲̼̪̱̋̄̊̓̒̔̄̂̏͠͠o̷̢͓̥͕̞̹͓͗͗̉͐̐̅̍̋̉̍̈͑͟͜ş̸͉̗̱̦͎́̈́̾͟a̷̧̧̛̱͖̠͕͓̫̻̠̝̦̬̳͑͑͋͂̀̅̽͂͘͘͝ͅt̵͍̹͇̼̩̲̙͉̻̤̻͊̅̎̐͟i̵̢̦͇̪̫͕͎̱̣̹̟̼̫̙͍͗͌͒͊̊̾ͅo̸̡̹̱͙͉͓̩̙͝͝n̷̥̫̄̆͘̚ş̶̨̮̭͖̤͎͓̺͕͇̟̥̄̉̄̃̈̌͒̔̐͡ ̵̛̟̣͔͍̈́̇̉̿̈́̿̈́͜͟͡ͅg̸̺͇͈̗̙͇̜͓͍͓͛͊̽͗͑̑̽͆̿͗̉ō̴̱̭̹̯͎̬̺̗͒̍̈́̈́̈̐͡ ̶̯̯̼͇̱̖̮̠̭̳̗̪̳̈́̍̉̎̈́̓͂̿̑̒̐̅̚s̷̖̮͖͕̗͙̗̈̋̄͋͜o̶͎͙̭͉̠̱͔̞̦̱̯̳͉̫͒͆́́̍͗̌̐̅̕͘m̸̧̢̭̳̱͕̖̜̬̺͕͎̲͛̆͛̑͑ę̵̫̗̳̠̓̾̓̈͘͟w̷̨̧̧̘̯͍͉̩͕͎̫͓͇̥̱̄̂̒͌̀̑̕͟͡ḩ̸̞̬͉͕̖̜͖̭̹͚͉̂͟͜ẻ̴̢̧͕̘͇͍̱̲̣̗͙̫̞̹̹̈́͆͊r̷̡̢̛̛̳̤̖͍̟͔͛̈̄̃̽̏͛̔͌͑̀͡e̷͈̙̲͓̼̥̟̭͕̭̫̯̯̅̈́̿̈́̑̎̄͑̒͐͜͟͝͝.̷̛͉̺͇́̈̂͊̋̓̈́̔

Your question is related to a very difficult interdisciplinary research problem: “how does ‘meaning’ occur in human conversations?” You can approach it from e.g. philosophical, psychological, linguistic, or sociological disciplines, and fields as diverse as literary critical theory, neuroscience, and artificial intelligence also have a lot to say about it.

So to answer your question: nobody knows for sure, but if you’re interested in academic pursuits you’re headed in a great direction.

Probably about 7. Give or take 10lbs.

Where did you get 80% from - is that based on something more than anecdotal?

A friend of mine, back when we got stoned a lot, had an idea that language, or words, are magic. Stringing together incantations to share thoughts is a neat way of thinking about it. Especially because we’re just jello trapped in a mecha made of bone and meat. It’s surprising there’s not more hallucinations to be honest.

Depends on how you define hallucination

Misremembering details, false assumptions about what is said, assuming intentionality incorrectly, projection of emotions onto others, bias, etc mean that the same words are said but we walk away with potentially wildly different interpretations of the experience

“Getting on the same page” is a challenge

Usually you dont need 100% of the information to get across and also sgouldnt expect it. When you want to make a point, you dont need every tiny nuance stored in your mind for that. The 80% is what you actually want understood, the last 20% are negligible.

But yes, the concept is interesting and in some cases a conversation is interpreted wildly differently between people, especially when you dont know the other person very well (e.g. someone might be intimidated by a stranger talking to them interpreting what they say in a negative way while the other person is trying to be friendly and wouldnt know how it is percieved)

TL;DR: Natural language is ambiguous. How much of it do we misunderstand?

There are many tools to reduce misunderstanding: feedback, rephrasing, definitions, etc., but it would be really cool if a standardized logical language (like loglan/lojban but actually well done lol) became the worldwide second language and lingua franca. That would help a lot in our increasingly vocal interactions with computers.