Why don’t you want me waving my knife at the spirits?
The Insular Celtic lore is very clear that “cold iron” is offensive to the Aos Sí. As the Aos Sí are variously seen as the Goddesses and Gods, the ancestors, and/or the spirits of nature, it is a bad idea to anger them. The idea of walling out spirits and attempting to command them with knives and swords is derived from Ceremonial Magic, and the traditions influenced by it, like Wicca. However, CR is built upon Celtic traditions like the living Fairy Faith, where we form relationships of mutual respect and hospitality with those spirits who are willing.