Let us see its evolution history first: (image get from http://www.vividict.com)
|Learn one Chinese Character a day - 入|
Before entering a house, we see its side view as . After entering the house, we are then covered by roof, and normally roof is more obvious than walls while we are inside a house.
Omitting walls of , we get, which is eventually simplified to current 入, and it means enter.
Now let us enjoy a Chinese calligraphy with 入 inside to end our lesson today: