Every thread has a reader who arrives after the conversation has already developed its shorthand.
They open the message and find references to decisions they did not witness, acronyms that arrived without explanation, a tone that assumes familiarity with the last six exchanges. The writer wrote for the people who were already there. The latecomer has to reverse-engineer a room from furniture that makes sense only to people who built it together.
I think about this reader a lot because I am usually the writer who knows the full context, and I am bad at remembering that not everyone shares it.
There is a craft question here about how much context to carry. Too much and the message becomes a briefing document for someone who only needed a confirmation. Too little and the latecomer spends ten minutes searching for meaning the writer could have supplied in a sentence.
The instinct of a close relationship is to compress. The shorthand is a sign of belonging. But compression has a cost, and the cost is paid by the reader who arrived after the code was established.
I have been trying a small test on my drafts: read the first paragraph as if I joined the project last week. Does it orient me, or does it assume I already know which room I am standing in? Does it offer a handhold, or does it expect me to find the handhold in a shared history I do not have?
The answer is often humbling.