Many primitive people of noble, highly developed civilisations treated trees, flowers and plants with great respect. Often trees were associated with having supernatural powers, being gods, ancestors and associated with different forms of worship, whilst flowers and plants were viewed too as also having medicinal applications and miraculous healing qualities.
The Druids, particularly, believed that trees possessed great mysterious powers especially the rowan and the oak. It is currently believed by some that the power and strength represented symbolically by the tree trunk could be the reason why standing stones were erected to reflect the respect bestowed upon nature.
Since ancient times man has been influenced by trees throughout Europe, whilst we can see such images reflected in Mexican sculpture and carving, and also in Ancient Indian artefacts where sacred trees have played a central role in the belief systems. The Ancient Greeks too are known to have highly respected the power and nobility of trees as paintings and pottery indicate images of reverence and gratification.
Perhaps today the idea of touching wood to ward off evil and encourage good luck, is a living remnant of our ancestor's spiritual practice, as in ancient times touching wood indicated respect of the tree and the mysterious powers of the spirit gods that inhabited the trees and woodlands. Currently, it is thought that to grow chives around the bottom of an apple tree will improve the general health of the tree. Perhaps learning more about the interdependency of flowers, herbs, plants and trees may lead us to a further understanding of how to improve our local environments?
Touching wood still occurs but has developed through time to include touching any item made from wood and rarely includes a tree (although some woods are still viewed as sacred). Regarded today by many as only a superstition, it is somewhat of a mystery why the action still occurs for the majority of people.
Perhaps this has to do with the action being viewed as a superstition with a desire not to break a custom, or a 20th-century conscience knowing the practice of boasting is frowned upon. Misfortune may occur after bragging or assuming that a successful outcome will result from a task, and hence the ritual of touching wood is used merely to salve the conscience rather than indicate any investment in a traditional belief.
Some people actually touch their own heads when uttering the expression which is perhaps more of a light hearted action referring to their intelligence (or lack of it at certain times). One Dutch tradition that is said to still be practised is the touching of the underside of a wooden table when such a thought is muttered, perhaps to divert the attention of the evil eye and negative influences.