The descent to the underworld can be distinguished from the night sea journey of the hero in many ways. We have already noticed the main distinction : the hero returns from the night sea journey in better shape for the tasks of life, whereas the nekyia takes the soul into a depth for its own sake so that there is no "return." The night sea journey is further marked by building interior heat (tapas), whereas the nekyia goes below that pressured containment, that tempering in the fires of passion, to a zone of utter coldness.
— James Hillman
The coldness Hillman names here is not a failure of the journey — it is its signature. This is the detail that most readings of depth psychology quietly skip past: the underworld is not a forge. Something in the psyche wants the descent to be transformative in the heroic sense, wants the suffering to be tempering, wants the heat of ordeal to guarantee a better self on the other side. That want is the night sea journey dressed in the language of soul-work. It is one of the psyche's most persuasive moves — if I descend deeply enough, I will not suffer; I will have suffered, and that past tense will protect me.
Hillman refuses the transaction. The nekyia does not rebuild the traveler. The coldness below passion's fires is not a stage before return; there is no return in the relevant sense. What this means practically is that depth work cannot be entered under the premise that it will eventually pay off in greater capacity for life's tasks. The zone of utter coldness is the soul's own country, entered for no yield. The reading of any genuine descent has to pass through that refusal of yield before it becomes honest about what it is actually asking.
James Hillman·A Blue Fire: The Essential James Hillman·1989