Why do you have to knock on the door three times to enter the hotel?

Metaphysics says: knocking on the door three times before entering the door is to tell the ghosts and gods inside that someone is going to enter, which is a sign of respect. Scientifically speaking: Generally, door handles are made of metal. Knocking on the door three times is to release the static electricity on the door to avoid being shocked by static electricity. Most doors open inward, so you have to bend over to get in. Because the room is a closed space, after opening the door, let the air (dirty things) in the room come out first and then go in. If you go in sideways, the air will jump directly on you.