Lock Around The Clock

They're refurbishing some of the apartments in my building right now, and today someone arrived to deliver supplies to one of those rooms.  Unfortunately, the delivery guy got the number wrong, and tried putting them in my apartment instead.  Of course, he figured out something was wrong when he tried to open my door and found that it was locked.  But it was an unsettling surprise to me to suddenly hear someone try opening the door without knocking first.

It's a good thing I remembered to lock the door, or it would have been more embarrassing.  Usually I do lock it, but sometimes glance at the door and notice that it's unlocked.  That makes me wonder, just how often does it really make a difference to lock it?  No, I'm not bragging about living in a nice neighbourhood where you don't have to lock the door.  I'm just marvelling at how society works.

Say I go away for a week: how likely is it that someone will actually try my door to see if it is locked?  Based on how many people have actually tried it while I'm here, I'd say it's likely that I could leave the door unlocked for that whole vacation, and no one would come in.  Again, it's not because everyone in the world is honest; it's because we expect doors to be locked.  So we don't actually have to lock our doors, but that's only because we always lock our doors.