A patient came to see the doctor. "Doctor, my tummy hurts"
"What did you eat today?" Doctor asked.
"A rotten apple." replied the patient.
Then the doctor gave the patient a bottle of eye drops.
"I have diarrhea. Why do you give me eye drops?" angrily the patient asked.
"I only treat the cause of the disease. If your eyes were good, you wouldn't have eaten the rotten apple." replied the doctor politely.