I am thanking everyone for their input!
Having contemplated aspects of this question on and off since 1965, I am going to try to explain what I feel is the greatest illusion. One of the fellows I use to kick this around with went on to work with Steve Jobs on the very first Mac computer. But Ed and I were just scratching around the edges of this.
I say that everyday, ordinary reality is he greatest illusion. And by this I mean the simple, straight forward reality that you and I normally experience in the course of a day: like sitting here typing this out; listening to the window a/c running; the pressure under my right forearm that is pressing on the counter; the large window in front of me; looking out at a bridge; streets; a tennis court; the cold air; the cold can of diet coke off to my right; feeling the seat press against me; etc.
So why do I say that this is the greatest illusion? But how to tell you so you'll understand? After all, my declaration is rather bold. I can challenge myself. I see the two-way radio and just now picked it up. It weighs about a pound and is black. I can see everything in this room; get up and touch everything, if I wanted to. All rock solid. A lot of the things in here I could throw in my truck and take them home. And they would be in my truck where I put them in the morning. All very normal. All dependable actions that myself and others rely on daily. I drive up to the stop light. Vehicles stop and go. Nobody runs into me. I don't hit them. Day after day, year after year, and yet, I still say that this is all the greatest illusion. Why?
I can only try to explain what I think. I hope you can follow me. I don't tell many people this. OK, this requires you to imagine something. Imagine total blackness. Now imagine a round, hollow sphere floating in the blackness. Make the sphere around 12 feet in diameter. Make it about 4 inches thick. We are not interested in the outer surface. Let's concentrate on the inner surface. Imagine that the inside surface is completely covered with a screen. Every inch of it; top, bottom, sides, etc. However, top and bottom doesn't even apply. OK, soon we are going to "TURN ON" this screen. I'll explain. You have to put on your "Star Trek" thinking cap.
This screen is not a man-made material like your computer screen, TV, or movie theater screen. Imagine that every aspect of this screen is organic. Nothing like you've ever seen (but see every day). Now imagine that the inside surface of this organic screen is full of different types of sensory units. Organic units. Imagine placing many organic speakers all over the inner screen. Organic surround sound. With your imagination, now place little organic air nozzles all over the screen (next to all the organic speakers), that puff out any conceivable order imaginable. Now imagine this inner screen made with an organic material that is kind of like memory foam. Very sensitive to touch. Now imagine that everything you have created so far also has a unique taste. But remember, we haven't "turned the sphere on," just yet. Now imagine that you have no body, but that you are conscious. Consciousness is an ability more than "a thing." So just BE inside the sphere and just be there. OK, now the screen is going "to turn on." Remember, you are inside, but you are not a thing to be in any particular place. You are just conscious of your surroundings.
As I said, right this moment I am sitting in this little air conditioned building (at a resort where I work). This is where I am right now. I get off in 3 hours. ...OK, back to the sphere. It is turned on. This huge organic screen of sorts "lights" up. I see a tennis court off to my left. A bridge with a black railing out in front. I am able to look in all directions. Every view is different. I smell something. I see hands in front of me on the keyboard. The keyboard is sensitive and I feel it. "Over there" is the smell of tea.
OK, I hope you get my drift. What I have been describing is my best attempt to portray what "scientist" say is going on in our brain. Think about it. EVERYTHING you see is a facsimile (picture) of "the real thing." But don't ask me where the "real thing" is because everything I see is a picture of "the real thing." I never see "the real thing." I never do. They tell me that the center of sight is located in the far back of my head. I guess on some organic screen. In fact, all the senses are "pumped" into my skull via nerves....all making up the organic screen I was having you imagine.
So they tell me this is true. What I see, I am actually seeing way back INSIDE my brain, not OUTSIDE the window; the bridge with the black railing.
Add all the senses to this organic sphere, called my skull, and years of thinking, "front and back, right and left, up and down, Oh, I see that brown car." But no. They tell me that is not THE brown car. What I just saw is a picture in my brain, of what we all call, "a brown car."
It just boils down to this (and you can apply and multiply this across the board): what we see is a picture. NOT the actually object. You have never seen an "actual" object, ever; not one time in your entire life. It is not possible. It is impossible. So-called light emanates from "the actual object," enters the lens of the eye, stimulates the optic nerve, impulses travel down this nerve into this organic sphere in the back of the brain and a screen "turns on." And like a fool,I am 100% positive that out there in front of me is a bridge. But out there is actually "in there."
This kind of puts it into words. Not even sure what to make of all of this. Heck, I can't get anyone to even understand what I am saying. Even so, call me a fool but this is why I say that "reality is the greatest illusion."