Underdog as usual hits the nail right on the head!
The 5 element theory in TCM was based upon the observations of the way the natural elements of the universe interact to form a whole. Each of the elements is dependant on it's neighbour in both the Constructive and Destructive cycles, along in my Shiatsu studies these are being referred to as the Nourishing and Controlling cycles (which in my opinion is a far more accurate translation based upon their functions). I done a post on 5 element theory basics a while back which describes the relationships of the elements here
PS. Kinda interesting reading back through the old threads and seeing how my perspective has changed. It's actually probably more in line with Kyushogits... shame he was a total twonk, he could probably have contributed quite a bit.