Unlike the lookalike 'person' kanji (人）, the top of 入 bends left, so you can say,
|( に / を ) い＊れる||
I put it in (I put the dog in the doghouse)
|( に / が ) はい＊る||
it goes in (The dog goes in the doghouse)
entrance (often shortened to 入口）
|に 入院 する||
check into the hospital - not for a simple exam, but like you have to stay there at least one night, you're too sick to leave.
|入||put/go in||TOP FACES LEFT|
|人||person||TOP FACES RIGHT|
The top of 'put in' faces left and - at least in larger fonts - the top little yoink of 'person' faces right.
That's because most people are RIGHT-wing bastards, and the bullets of the LEFTIST, glorious people's revolution will enter the LEFT side of their heads. !Viva Mao!