carry coals to Newcastle
US /ˈkæri koʊlz tu ˈnjuːˌkæsəl/
UK /ˈkæri koʊlz tu ˈnjuːˌkæsəl/

1.
多此一举, 画蛇添足
to do something that is unnecessary because there is already a lot of it available
:
•
Bringing more blankets to the shelter would be like carrying coals to Newcastle; they already have plenty.
给收容所带更多毯子就像多此一举;他们已经有很多了。
•
Offering him advice on coding is like carrying coals to Newcastle; he's a renowned expert.
给他提供编程建议就像多此一举;他是一位著名的专家。