This patient goes to the doctor to get a prescription, which the doctor writes out in the usual illegible handwriting. Seems the patient, having put it into his pocket, forgot to have it filled.
Every morning for two years he showed it to the conductor as a railway pass. Twice it got him into the movies, once into the baseball park, once into the symphony. At work he got a raise by showing it as a note from his boss.
One day he misplaced it. His daughter picked it up, played it on the piano, and won a scholarship to the Faculty of Music.