I guess the issue here is one of cosmology. The difficulty for the Western Mind in all this is how it is trained to perceive itself as a distinct and seperate entity from all other energies.
In that paradigm, we are perceived as being connected essentially to an almost infinite number of other energies which go together to make up our universe. So, while we may operate as individuals, with individual identities, we are at the same time functioning as part of a larger, interconnected whole.
Most people can accept that interconnectedness as a reasonable feature of our basic human cosmology, but their egos balk at taking it into their conciousness as a functional reality. After all, if you really accept that premise, western culture gets turned on its ear. Things which we prize now in our cultural context become worthless, and others, which seem to have no real value, become highly desirable. So, following the western paradigm one's mind will only go so far. You can see in this line of reasoning, a person from that culture would necessarily find it difficult to perceive how part of a person's soul/energy could actually become seperate from them.
The shamanic paradigm, or cosmology, is radically different in many ways. Shamans are, in a very real sense, highly trained specialists in 'seeing' the connections people have to the world energetically. They see not only the main points of connection and expression, which almost anyone can learn to work with, but they also see the billions of other connections people have as a matter of just being alive in our world. Each of those connections is unique and represents a different aspect of our life experience. They know that energy movement is not a one way street - it moves in its various types both ways, into, through and out of our energy.
Soul retrieval as a concept makes perfect sense in this paradigm. Perhaps soul retrieval is a poor choice of words, it is more akin to a part of your energetic ability to be aware. Awareness is at the crux of what we are as human beings. Most people associate the term soul retrieval with severe trauma or abuse, but soul or energetic loss can also occur over a long period of time under almost any given circumstance. Shamans recognize this in people when they see in them areas which are no longer functioning, or functioning in very distorted ways. The question for shamans over the last several hundred thousand years has been, where does it go? Where have these connections and parts of awareness disappeared to? Where are they hiding? Over time they became aware that these 'parts' of a person were no longer within the person's normal sphere of influence or awareness. They were outside the ability of the average person to call back into their awareness. Simply put, these energies had moved out and along some of those lines mentioned before into places no sane person would ever think to look.
Since shamans are by no means considered 'sane', they started to hunt for them. The different shamanic traditions all developed myriad ways of helping people recover this errant energy. Common attributes of these methods revolve around a specialized 'journey' the shaman undertakes to find this energy and coax, push, or pull it back to the individual. The results of recovering awareness and these connections can be quite startling to the individual being helped. The nature of the jouney itself and how it is presented in translation into understandable terms are extremely varied, but in the hands of a 'big' shaman, they can be intensely effective. One must consider always the possible ramifications to the individual in their day to day world.
Consider only one possible scenario, a person who has at some point suffered sexual and or emotional abuse as a child. The shaman sees the distinct damage this has caused and undertakes the journey to bring back to them their energy. Imagine the rearrangment of the person's energy in order to fit this back into the whole. The results could be devastating if the person is not working with someone who is properly trained and prepared. People need to be careful opening themselves up to all the self styled shamans out there today. Anyone who tells you they can do a soul retrieval long distance is not only a fool, but a person who cares little about the other person's well being, preferring instead to stroke their own ego with a sense of power.