A Swiss couple on vacation in India found a beautiful picture in a store. They bought it, and in order to protect the picture the store-keeper rolled it up and slotted it into a long cardboard tube.
The couple continued to travel around India and so for the rest of their journey they had to carry the tube everywhere they went. It was long and awkward, and they were forever trying to protect it, to stop it getting bent or dented as they climbed into buses, or clambered out of rickshaws.
Eventually they took the tube home to Switzerland where they opened it, only to discover that the store-keeper had deceived them — he had never put the picture inside. All the time they had been carrying around an awkward tube, trying to protect it, when really it was empty!
At first they were angry, but then they laughed.