get through thick skull
get (something) through (someone's) thick skull
To make someone or oneself acknowledge, accept, or understand something when they are or are being obtuse. Look, just get it through your thick skull: we're moving, and there's nothing that's going to change that now. I don't know how else to get it through her thick skull that I want to break up.
get something through someone's thick skulland get something into someone's thick head
Fig. to manage to get someone, including oneself, to understand something. He can't seem to get it through his thick skull that he has to study to pass the exam. If I could get this into my thick head once, I'd remember it.