Close your eyes now, and try to imagine yourself lying on the floor, and you will see what I mean. This is not the only difficulty. Any visualisation that requires you to imagine yourself at a different place from where you actually are is unnatural and hence extremely difficult. This, I believe, is the cause of most failures. A great deal of energy is wasted on this, energy which can be better used on the projection itself.
Visualisation is a big hurdle for people when they are learning to project.
Many have trouble with it because they think they have to actually SEE what they are visualising, you DON'T. People who can visualise things clearly DON'T actually see anything. If they do, it is no longer a visualisation but a clairvoyant vision. Visualisation is simply the ability to construct a representation of what something would look, or feel like, in your minds eye. It is better termed fantasising, an imaginary perception of reality. Many people who say they can't visualise at all, are still able to create elaborate fantasies.