Sharing requires having one's pieces of information open/closed.
So, shared means (first) under version control (a weaker form is possible with news when the selector for the information item is matched to a thread instead of to a given article)!
Also, sharing is incompatible with ownership (the opposite of sharing is splitting): once information is shared, it is not owned by anybody. This works both ways:
Note also that it doesn't mean that one would assume that people are replaceable. Only that after one has done something, what was done should be understandable and reproducible by the others.