go against the grain

Something go against the grain when you find it difficult to accept, or do, it because it opposes a belief or principle that you hold.

违背本人的意愿。

A lie went against the grain, but it was necessary.

撒谎违背我的意愿，但又是必要的。

On a piece of wood,the grain is the natural patterns and lines on its surface. It is easier to cut with the grain than against it.

grain指的是木头表面上天然的纹理。顺着纹理劈木头比较省力。