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.

Common Names:

Name	Pronounced	Usage
Deonte	-	African American (Modern)
Floortje	FLO:R-tyə	Dutch
Marnie	['ma:ni]
Motel	-	Yiddish
Early	['ə:li]
Jehan	-	Medieval French