Reportedly, in small towns, people don't lock their doors much. In cities, we do. In college I had a friend who didn't lock her dorm room, which struck me as weird (though I happily took advantage to drop off surprise flowers.) Sometimes I've wondered about the need for locks; I'm home a lot, and it's not like people come to try the door. (Of course, I live in a good neighborhood.) And it'd probably look weird to go down a street or hallway trying door after door.

But, of course, if no one locked their door, you could just go to any home that looked empty and enter to plunder it. It's the fact that everyone locks their door that means an individual can get away without it, like skipping on vaccination if everyone else gets shots.