A man went to the doctor complaining that his knee was in pain. The doctor examined him for a while before sitting back in his chair.
“I’m afraid it’s just old age. There’s nothing we can do about it.”
The man shook his head angrily, saying: “That can’t be! You have no idea what you’re doing.”
“What makes you think I’m so wrong?” The doctor replied.
The man yelled back: “It’s obvious. My other knee is fine and it’s the exact same age!”