I’ll go first:
The Convention:
Passivity, quietness, and docility constitute good behavior.
This is not a prominent convention anymore, but far from obsolete either—especially in regards to pets and children, and, more glaringly, to wives and servants. You can hear it expressed in the saying “They behaved so well it was like they weren’t even here,” and in the blunter saying “Children should be seen and not heard.” I got to thinking about this a little while ago when I jokingly thought to myself that our dog, who isn't here, was being "so quiet it was like he wasn't even here."
The underlying implication seems to be that servile humans and creatures, when in the presence of their masters, should be “at the ready” or otherwise “not a nuisance,” thus implying the preclusion of their more natural state of behavior.
I don’t want this thread to imply that every questioned convention is worth rejecting. That said, this convention seems very difficult to justify as generally valid, and is definitely something to keep in mind the next time you find yourself being meeker or more polite than you would otherwise be—or demanding the same from others.