Chats are append-only logs of messages because it's hard for the human to absorb changes in the conversation.

Humans don't re-read every previous message of the conversation before responding; they use their imperfect fuzzy memory of what's already been said.

But LLMs don't do that at all.

LLMs "read" the whole context for every single token they produce^[ahf].

Which means that as a modality you totally can go back and amend, tweak, edit the previous messages to give better background context.