Consider that there is a life force or soul of individual consciousness within your body, this level usually remains in the body and sometimes disconnects during "astral" or near death experiences. Some people are able to consciously develop it & control it.
It's really all about consciousness, there's DNA RNA encoded memories and they are the program of creation and life that is a cellular sort of consciousness. There's a natural life force that only wills bodily survival, a subconscious linking to that and the regular consciousness. Regular consciousness can somehow at times link to even higher levels. The highest Unity of all levels is what mystics refer to as God or Cosmic consciousness.
You can also think of it this way, your body is a physical light bulb, the electric is cosmic life force, and the light produced is consciousness. There are many colors of light depending on the type of bulb some are "astral".
There are many different and lower & higher levels of this experience and the proof to yourself is when you discover something you perceived in this state REALLY happened. It's a very personal and spiritual event that changes your whole perception of life. It's very difficult to even connect to your own subconscious and understand consciously so you can imagine how hard it would be for someone to connect to the higher levels without much experience. Sceptics don't believe it or try to comprehend it, but who cares if they don't?
I will give another parable like explaination why most people can't do it or just reach the level of lucid dreaming which is the beginning of connecting to the subconscious.
These fields of consciousness act are like a worm that develops into a butterfly more or less and the body is a caccoon.
While a worm you crawl and eat of the leaf but after the death like experience in the caccoon you become the butterfly that can walk, fly and eat of the nectar! Not all worms live to become what they were meant to be, They just go from egg to worm because they die before they become a butterfly if you know what I mean. There's a lot of mystical symbolism about death and ressurection in so many cultures that is actually referring to this evolution of the soul that can free of the body even before death.
I think most people who sincerely want to try it make the mistake that they are trying to leave the body when you are really just trying to expand this field of consciousness to encompass a larger area outside of the body.
If you see with your eyes have you really left where you are?
If you are blind does that mean others can not see?
You have to go into the center of your being in order to connect to a larger field of consciousness that unifies these other different levels of consciousness and life force fields.
It is much harder to develop a field that "disconnects" from the center and actually goes out more or less seperately.
I think many who fail to experience the astral level, it's because they are trying to fly before they grow their "wings" then wonder why they can't do it!
You have to go within to the center and connect before you can "project " into the higher levels consciously. Mystics sometimes refer to this as connecting to the "heart" center and taking it to the "third eye".
Thanks for this post, it means a lot to me...