For most of history, people experienced woodland as a frightening wilderness populated by dangerous species and ghosts. You could get lost, starve, freeze to death, or killed by brigands and wild animals. In Jung's psychology, the forest represents the feminine and the unconscious, which is associated with the mysterious, adventurous, and demonic. It is a place of ordeal and initiation, which the protagonist must live through to grow spiritually. You can disappear there, but in case you return, you will be changed forever.