Because there is the spirit of tree within a tree

Because there is the spirit of tree within a tree, therefore its flowers blossom fragrantly, it turns green, its branches and leaves flourish; this is called the marvel. Even though you may break wood down, you do not see anything you may call the spirit of tree; yet if there were no spirit, the flowers and foliage would not come out. This is also true of the human spirit; even though you cannot open the body to see something you may call the spirit; it is by virtue of the existence of the spirit within you that you perform various actions. --Mayamoto Musashi, The Book of 5 Rings, Shambhala Publications