From Wood we get Fire. Fire cannot exist by itself but is produced by burning wood. From Fire we get Earth. Symbolically fire reduces everything into ashes, which becomes part of the earth again. From Earth we get Metal.
All metal has to be extracted from the earth.
The entire universe is composed of these five elements. They are interdependent and each is controlled by another. Metal can only be melted and forged with great heat. Fire is controlled by Water. Nothing will put out a fire as fast as water.