Nobody has a perfect memory. Single people forget too. We know a lot of older people-- and some younger people-- who have to keep constant notes to remind themselves of everything because their memory isn't very good.

Some systems who do lose time communicate by leaving notes for each other. Some systems who don't lose time communicate by leaving notes for each other. In both cases, it's still a form of communication, and therefore responsible. If you have no communication system at all, not even notes/letters or one person who remembers things others don't, then that is a problem. A communication system does not have to include sharing of all memories. But there should be something.

-Lilac