헛걸음하다.

on a fool's errand

Bill went for an interview, but he was on a fool's errand.

The job has already been filled.

[Bill은 면접 보러 갔는 데 괜한 헛걸음을 했다. 이미 사람이 구해져 있었다.]

I was sent on a fool's errand to buy some flowers. I knew the shop would be closed by then.

[나는 꽃을 사러 가서 헛걸음질만 했다. 나는 그 가게가 그 때 되면 닫는 다는 것을 알고 있었다.]