◆to bang your head against a wall or to bang your head against a brick wall<非正式>碰壁；徒劳
I appealed for help but felt I was always banging my head against a wall.我恳求帮助, 却觉得自己总是处处碰壁。
I wondered if I was banging my head against a brick wall.我不知道自己是不是在白费力气。