get (something) into (one's) thick head
To make one acknowledge, accept, or understand something, especially when they are being obtuse or willfully ignorant. Look, just get it into your thick head—we're moving, and there's nothing that's going to change that now. I don't know how else to get it into her thick head that I want to break up. I don't know why I'm having such a hard time getting this equation into my thick head.
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