An elderly gentleman with failing eyesight checked into a hotel room, carrying a bottle of wine in each hand. On the wall, he mistook a fly for a nail. The moment he tried to hang the bottles on it, they fell and shattered, spilling wine all over the floor.
A waitress discovered the mishap and, feeling deep sympathy for him, decided to help. The next morning while the old man was walking in the roof garden, she hammered a nail into the exact spot where the fly had been.
Later, the old man returned to his room. The smell of the spilled wine reminded him of the accident. Looking up at the wall, he saw the "fly" there again! He crept closer and slapped it with all his might.
Hearing a loud cry, the kind-hearted waitress rushed in. To her astonishment, the poor old man was sitting on the floor, teeth clenched and his right hand bleeding.