Elevator doors won't open unless a little sensor indicates that the floor of the car is lined up with the floor outside of the elevator. If that switch is old and worn out, then sometimes the door stays shut. If you jump around, sometimes the switch moves just enough to make the elevator believe that alignment has been achieved and allow the doors to open. Elevators are cool when they work, and can be lethal when they malfunction. If the doors open when the car is between floors, don't get out! We've all seen that movie, right?
