I don't intentionally left the key, I already beat the game many times, I'm reporting a bug here. If you play normal game, most people won't come to that circumstance as usually there are still spaces in inventory. But recently I just tried playing nightmare mode and I had full inventory due to the amount of items (phone, camera, axe, tape, package, glock). To get the basement key at that time I have to drop an item, and it would be glock as it's least useful. But then I was thinking if I can go back to take the glock again, and then I aware you can't go back to that room anymore.
So if you drop an item at that room and go down the rope, you will never retrieve the item anymore. If the dropped item is the basement key then you will become stuck. A good designed game should prevent this to be happened.