Thus although we already know that it contains all the different interconnections, the radiation itself nevertheless stands in such a way that it is impossible to understand. First it appears one way, then differently. As a result, the way it governs is unknown. For if we were to try to follow a single thing that exists below in Atzilut and trace its root in this Head, we would not be able to find our arms and legs – we would be unable to determine anything about it. First it appears like this, then it appears like that – in such a way that it is quite impossible to understand it. This is why it is called the Unknown Head.
Life of Unknown Head
Kalach Pitchei Chokhmah 88:3