lost cause

1. N-COUNT If you refer to something or someone as a lost cause, you mean that people's attempts to change or influence them have no chance of succeeding. 必敗無疑的事; 無望成功的人

They do not want to expend energy in what, to them, is a lost cause. 他們不想把精力投到他們認爲注定不會成功的事中去。