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."
See also: get, head
Farlex Dictionary of Idioms.

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.
See also: get, head, take
Farlex Partner Idioms Dictionary
See also:
  • get (something) into (one's) head
  • get something into your/somebody's head
  • take (something) into (one's) head
  • take into head
  • take it into your head
  • What number are you calling from?
  • candy-coat
  • expose (someone, something, or oneself) to (someone or something)
  • expose to
  • catch wind of (something)