get/take it into your head that...
get (something) into (one's) head
To believe that something is true. Get it into your head: I'm in charge until Mom gets home, so you have to listen to me. A: "Why is Johnny holding his breath?" B: "Well, he's gotten it into his head that holding his breath will make him taller."
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
get/take it into your ˈhead that...(informal) think or believe something, often wrongly: Somehow she’s taken it into her head that her husband is trying to poison her.
Farlex Partner Idioms Dictionary © Farlex 2017