From ancient times dreams were a source of fascination for human beings; made him believe that beyond this world that everything is solid, harsh, irreversible and hurting there is another world where impossible easily can become possible. One could see he falls from the cliff but he wakes up safe and sound without any bone broken. Hence, there is another world somewhere out there that should be searched for. Only that one needs to find a way. But, wait a minute! Why such a world, the world he sees in dream, is so hash-mash and mishmash, so randomly patched?
Humans used to believe that dream is a door to beyond open to them. He believed it is his soul, his spirit, some etheric intangible entity, that is not vulnerable to harshness of material world, and in contrast to it, that can be separated from his body and easily can travel into and experience the other worlds and even might be able to carry his body. Who, then, interprets these things, these sceneries that man beholds?
The key answer and key of messiah psychoanalyst is this : interpreter is the "mind" of human. So there is mind and there is dream : two things. Mind watches the dream or has to watch the dream helplessly. Human can observe that he cannot control flow of dreams and while he is watching the dream - and he believes he is in dream - he has not power to assert himself and is not able to change its course.
There were reasons that man believed dreams should be part of him. He had day dreams, too. He used to sit on the side of the cliff and to imagine that he could fly over to other side of the gorge. He loved to immerse in the raging waves and could breath and swim and come alive from the other shores. He had a wish that he could beat the ruler down in face of his injustice to become the ruler and to rule with all justice. He could understand that these are all just day-dreams and at the end of the day he has to tolerate all miseries for a piece of rotten bread. Therefore, dreams, when he is sleeping, are part of his wishes similar to his daydreams; he speculated.
Again the key predicament, I put extend forward, is that he is able to stop the daydream and control it and revise and change it and make himself the winner of wishes in his imagination and even makes it true by personal strife and struggle, all in contrast to what the "night" dream is.
Man also believed that as having mind and soul is endowed only to humans then only humans, and no animal, can have a dream.
Interpretation of dreams started to become part of endeavour of humans and in particular part of commitment of medicine men, priests and witches.