10,000,000 : 1 shots do happen however. About 20 years ago a hunter shot at a duck on a lake. He missed, and the bullet hit the water just right and ricocheted.
1/2 mile or so away a car was traveling down the freeway. The bullet entered the passenger window (which was open) and killed the driver, piercing her temple. They figured had the window been closed, the bullet wouldn't have had enough power to penetrate the glass and kill her.