John and David were both patients in a mental hospital.
One day, while they were walking, they passed the hospital swimming pool and John suddenly dove into the deep end. He sank to the bottom and stayed there.
David promptly jumped in and saved him, swimming to the bottom of the pool and pulling John out.
The medical director came to know of David's heroic act. He immediately ordered that David be discharged from the hospital as he now considered him to be OK.
The doctor said, "David, we have good news and bad news for you! The good news is that we are going to discharge you because you have regained your sanity.
Since you were able to jump in and save another patient, you must be mentally stable.
The bad news is that the patient that you saved hung himself in the bathroom and died after all."
David replied, "Doctor, John didn't hang himself. I hung him there to dry."