A man drives by a mental state hospital

      Jones is driving past the state mental hospital
      when his left rear tire suffers a flat. While Jones
      is changing the tire, another car goes by, running
      over the hub cap in which Jones was keeping
      the lug nuts. the nuts are all knocked into a
      nearby storm drain.

      Jones is at a loss for what to do and is about to
      go call a cab when he hears a shout from behind
      the hospital fence, where one of the inmates has
      been watching the whole thing.

      "Hey, pal! Why don't you just take one lug nut off
      each of the other three wheels? That'll hold your
      tires on until you can get to a garage or something."

      Jones is startled by the patient's seeming rationality,
      but realizes the plan will work, and installs the spare
      tire without incident. Before he leaves, he calls
      back to the patient. "You know, that was pretty
      sharp thinking. Why do they have you in there?"

      The patient smiles and says, "I'm in here because
      I'm crazy, not because I'm stupid."