I heard a great anecdote years ago from a flatmate I had briefly; she was Australian but her mum was Malaysian. Her friends - being nicely brought up in Australia, which has lots of similar mores to Britain - finished the platefuls they were served by her mum.

In Malaysia, apparently, to finish a plateful given to you by your host means you are still hungry and have not had enough to eat. So they got given bigger helpings...

And so it spiralled.