（为了成功必须经历的）单调乏味的苦差事the basic, hard work, often physical or boring work, that is necessary for something to succeed
As an apprentice, you start out doing a lot of the grunt work. 作为一个学徒，一开始的时候你需要做很多单调乏味的苦差事。
A computer can handle the mathematical grunt work. 计算机可以处理这些单调乏味的数学工作。