Other than not knowing how to open the door, remembering to lock it, or r remembering to shut the door, some people can't tell if arestroom is occupied, they keep wrestling with it.

Even if it appears unoccupied, I always knock first, just in case someone inside forgot to lock the door. It's common sense.

Whether it's in an aircraft, airport, a lounge or any public place, it's usually easy to tell if a lav is occupied without pulling/pushing or wrestling with the door.

If you can't tell whether it's occupied or not, knock gently. This way you can prevent an embarrassing situation inc ase someone forgot to lock it the door, or if the lock is defective.