When backing a car, bus or straight truck, you first turn the steering wheel in the direction you want to go. But if you try that with a tractor-trailer, the trailer will pivot on the fifth wheel, and its rear will end up pointing in the wrong direction. When backing a tractor-trailer, you first turn the steering wheel in the direction that is opposite to where you want to go. The trailer will pivot, and its rear will end up pointing in the direction you want to go. Then turn the steering wheel the other way to follow the trailer, and continue backing.