Yin and yang are just generic words that symbolise opposites and can be applied to anything. Think of a water pipe with huge pressure. If there was a valve like a gate that was hinged on one side, you would never close it, because you are attempting to drive the whole gate against the force. If you move the hinge to the center, the valve is neutral to the force because it contains a balance of yin and yang and is free to turn, despite the pressure. This is a very crude example however. O'Sensei followed a religion that believed the universe was created from yin and yang. If you move this way their force is met with the forces of the universe, leaving you free.