Here are some Frequently Asked Questions (but not really) about the esteemed art of door politeness:
A: It's the art of being nice to the door when you're on the other side.
A: While it can be applied to openings of all kinds, the term "door" is specifically reserved for entrances that lead to places you want to get to, but aren't really sure you should.
A: Of course, but it's most effective with swinging doors, sliding doors, and revolving doors. Try to be polite with revolving doors, they get dizzy easily.
A: In that case, it's best to knock politely and hope someone on the other side is feeling generous. Don't forget to bring a nice gift, like a bottle of wine or a pie.