Insane or stupid?

His car had a flat tire in front of a mental institution. He pulled the car over as far as he could off the highway. There was a steep cliff on the side of the car with the flat tire. There was a patient sitting on the porch watching him change to the spare wheel. When he removed the wheel with the flat, he kicked the wheel nuts off the edge of the cliff and they rolled down out of reach. He had to get some more nuts, so he asked the patient on the porch if there was a phone he could use to call the Auto Club for help. The patient suggested that the driver take a nut off each of the other three wheels and replace enough nuts to get to a place where he could get some more. The driver said that was a brilliant idea, and how come he was in this institution. The patient said that he was insane, but not stupid.