頭あたまに入はいる

expression, godan verb (-ru)

understand; comprehend; get into one's head

Used when knowledge or information is successfully understood or retained. Often implies the information 'enters' the mind naturally or after effort.

• この説せつ明めいでやっと頭あたまに入はいった。

  With this explanation, I finally understood it.

• 一いち度ど聞きいただけでは頭あたまに入はいらない。

  Just hearing it once doesn't make it stick in my mind.