When you look at the light coming from a projector, the image it casts can be focused on the surface its aimed at to create a 'projection'.

The projection sits on the surface, creating an image 'plain'.

If you were completely unfamiliar with the physics of light and the mechanics of projectors, and you were to walk up on a projector casting a projection, you would have absolutely no reason to believe that one had anything to do with the other.  - It would probably appear to you that there was a projector that was separate from the projection...

 

It might appear to you that the 2 things exist completely independent of one-another, unless for some reason the beam was interfered with.

Maybe the relationship between our thoughts and our realities work much the same way.  This is why it's so confusing...

We can't tell that they are interrelated because of our current understanding...