Original fictional legend. No real location or event is claimed.
The rule is not that you must never knock on the locked room. The rule is that you must count your knocks. Three is safe. Four is an invitation. Five means you have forgotten which side of the door you are on.
The first caretaker wrote this on a strip of paper and hid it inside the key cabinet. The second caretaker crossed out the word safe. The third removed the door.
For a while that seemed to work. The corridor ended in a clean rectangle of plaster. People passed without slowing. Then someone hung a picture there, and the frame began tapping against the wall.
The new caretaker took it down. Behind it were five small marks. He touched each mark with a fingertip, counting under his breath. From somewhere very close, a voice said, “Thank you.”
The corridor has a door again. If you visit, do not stop to read the strip of paper tucked underneath. Reading takes time. Whatever is inside is learning to count the pauses.