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
Zlatko	-	Croatian, Serbian, Slovene, Bulgarian, Macedonian
Vincenc	-	Czech, Slovene
Aran (1)	-	Irish
Rachel	RAY-chəl (English), ra-SHEL (French), RAH-khəl (Dutch)	English, Hebrew, French, German, Dutch, Biblical, Biblical Latin, Biblical Greek, Biblical Hebrew
Amor	-	Roman Mythology, Late Roman, Spanish, Portuguese
Reuel	ROO-əl (English)	Biblical