Definition
To do something unnecessary or redundant; to do something pointless because it is already abundant in the place or with the person you are giving it to.
多此一举
Trying to teach him how to use a computer is like carrying coals to Newcastle; he's a computer expert.
试图教他如何使用电脑就像是把煤运到纽卡斯尔；他已经是电脑专家了。
Selling water to the Amazon rainforest is like carrying coals to Newcastle; water is abundant there.
向亚马逊雨林卖水就像是把煤运到纽卡斯尔；那里的水资源非常丰富。
Buying him a book on photography would be like carrying coals to Newcastle, as he already has dozens.
给他买一本摄影书就像是把煤运到纽卡斯尔，因为他已经有几十本了。