On most days, the function of a truck’s emergency brake is to prevent an emergency from happening.
But then there are those days when you’re out replacing window panes in an unfamiliar part of town, and the brake of the truck that you’ve parked in a tight alleyway just happens to fail – seemingly out of nowhere! Then, your truck just rolls backwards down the alley, miraculously without hitting anything, until it picks up enough speed to surprise the man at the far end of the alley.
Those are the days when you know you’ve gotta trade your emergency brake for a trip to the emergency room. Or the coroner’s office.