There are two sort of perspectives relating to perception that we seem to fall into.
1. There is an objective world with our perception OF it, and what we project ONTO it is to do with how we interpret it.
2. There isn't an objective world and we're just dreaming it up and not projecting anything "onto" it because we're projecting IT in the first place.
I am coming to see that neither of these is correct.
There is a third possibility.
3. I am having a dream, which is surrounding me with a fictional environment which is coming from my mind. Without my dreaming of it - my projecting it - there wouldn't be any world here at all. There is NO objective world. There is ONLY a subjective world. My projection makes my perception and makes "the world I see."
The important distinction here is that the world I am projecting/dreaming, is coming from my mind and SEEMS to be an objective world. AND yet at the SAME TIME, this world is being projected BY me. So it seems to be both objective and subjective.
The key is that the objective part does not exist at all, and that's what ACIM means by "there is no world apart from what you wish", and wishes are dreams.
So it's not just to do with hey, I'm projecting something "onto" the objective world. It's that literally I am projecting the world ITSELF - that I think is an objective world - with my dreaming mind. And when my mind dreams of a different world, I project out an entirely different world. The old world doesn't transform because it has no objective reality or continuity of its own. I just project a different dream and stop projecting the old one.
When we go into false perception, however, there is an additional LAYER of projection, which seems to project "onto" the dream. Like, you're filled with anger and hate and so this seems like it projects "onto" the objective world. But the objective world itself is still being projected from your mind at that same time. So in truth, you are not really projecting ONTO the world, you are projecting the world and your "bad projecting" is actually changing the world and making it appear like a bad world to you.
In this way, it would appear that ACIM is never really talking about "projecting onto" anything. It's entirely talking about you projecting the world itself, directly, and your "bad attitude" projects what later is perceived to be a world that you seem to experience in a negative way. You think there is some other objective world that is "not negative" hiding underneath your negativity, but there isn't! You think you're projecting ONTO the world, but in fact you're not. You're projecting the world, period. Projection makes perception. Not "projection makes perception makes projection makes perception."
Just as at night when you dream, your mind forms en entire environment/world filled with buildings and people and stuff, and you seem to show up as a single body person. But your mind is making the world AND your body person. How the body person seems to experience the dream is an illusion because the person is actually MAKING the environment. Any attacker in the dream is you. People in the dream are figments of your own mind. It's the same with "waking life". We are literally dreaming of an entire universe.