living with a door unlocked

I have totally forgotten this experience.
I wonder how many Hong Kongers have the experience of living with the door unlocked.
I am one of the lucky people. I know if I ask people to try to leave their front door unlocked, they will find  it ridiculous or too dangerous or even unacceptable.
This is exactly how I felt. I do agree it is not worth trying in Hong Kong. But I actually forgot it is possible somewhere in this World and I actually did.
It was in the UK. I was living in a house and never bother to lock the front door.
Somehow I do feel sorry about the social security of this modern world.