knock (one's) head against a (brick) wall(redirected from knocked your head against a brick wall)
knock (one's) head against a (brick) wall
To attempt continuously and fruitlessly to accomplish some task or achieve some goal that is or seems ultimately hopeless. I feel like I've been knocking my head against a brick wall trying to understand this math equation. Some people are never going to agree with you on this, so it's no use knocking your head against a wall trying to convince everyone.