Do something in vain

Definition: do something with no reason or chance at success

定义：徒劳地做某事

Peter feels his doing the job in vain.

皮特觉得自己做的工作是徒劳无效的。

Never feel you're doing something in vain. There's always a reason.

不要觉得你在徒劳地做某件事。事情总是有其存在的理由的。