Cách sử dụng
The expression "carry, take, etc. coals to Newcastle" means to do something pointless or unnecessary. It comes from a time when the city of Newcastle in England was famous for producing huge amounts of coal, and it didn't make sense to bring more coal to a place that already had so much of it. So, if someone says you are carrying coals to Newcastle, they mean you are doing something that is unnecessary or redundant.