Ah, but you can.

Really now? There is something I could say to prove that not everything is in your head? But your brain relays all information. Processes it all. Your whole life could theoretically be a construct, and I might not exist, and this conversation is happening because your brain is thinking those thoughts and projecting it onto others. There is no observation that does not go through the brain to be processed, so technically everything could be a figment of your imagination.

If you are real, and not a construct of my mind, then you can not form and bend to my will. If everything was an illusion, I would posses the power to form anything I wanted, because all everything else is what my brain is perceiving. Just thoughts. I could use my thoughts to project anything. I would not be bound to the laws of the universe. I could defy gravity, make energy and destroy it, I could move without being acted upon by an outside force, etcetera. I could even deform the molecules of concrete items, and simply turn them into matter, ready to bend to whatever my mind wants to project. After all, all that I would be perceiving would just be thoughts, and so all I would have to do is think what I want.

Not necessarily true. It can be in your head without you being conscious of it, like a dream. You mind created the rules for the dream, and you followed it. For all you know, you could be in a coma right now, or be on your deathbed, having a dream that is out of your control. There are many more outrageous solutions I could offer as well, such as you being in a Matrix type dream. But there is something more realistic that may help me prove my point. People have been known to have hallucinated people, things, and situations. A great example is in the movie A Beautiful Mind. A man spent most of his life thinking his college roommate was real, but in fact he had never existed in the first place. For all you know, this could be a mass hallucination, or like I said, dream. Because your brain will have created this whole environment for you, and there is nothing that is safe from being altered, because everything you ever know is the result of the brain processing it in the first place.

I loved that movie