Your mind simulates external reality even if external reality isn’t in and of itself a simulation. Even if you are convinced that your external reality is THE reality, you’d be wrong. So why is your version of reality any more real or accurate than that of any other species? You may think you know reality but from the point of view of every other species your reality is NOT their reality. Anyone who doubts that should read the famous philosophical essay “What is it like to be a bat?” (In “The Philosophical Review”, October 1974) by American philosopher Thomas Nagel. Other species aside, and by the way their version of external reality isn’t any more correct than yours is, why is your reality (and their reality) still a simulated reality?
Watching the monitor on your desktop PC / tablet / smart-phone, or a show on your TV, or a movie on the silver screen, you are viewing a simulation. Even in a real-time live-action event, say a news broadcast or a sporting contest, you’re not actually seeing the real reality or the real people up-close-and-personal, just a simulation composed of electrically-generated images.
Alas, even up-close-and-personal reality is also a simulation. You’ve only ever experienced a simulation. That’s because each and every thing you have ever experienced has been experienced inside your mind even though the actual reality, the stimulus, was outside of your mind. So your mental experience is once, twice, thrice removed from the actual stimulus. You have to have absolute faith that the translations from external reality to internal reality is totally accurate, yet you know that isn’t always the case (advanced age, drugs, injury, disease) and in fact can’t be the case since your mind differs from every other mind that has been, is, or ever will be. No two minds and associated brain chemistries are ever 100% identical, therefore your reality is actually quite unique to you and you alone.
Let’s imagine a woman, let’s call her Jane. She’s been married to Clive for say 40 or so years. Jane obviously believes that she has experienced Clive, warts and all. Wrong! Jane has never seen or heard or touched or smelled or even tasted Clive. Take sight. Jane has never seen Clive, only the photons* that have reflected off of Clive. In fact Jane hasn’t even directly seen and experienced the photons since they cease to have impact once reaching the optic nerve. The translation continues now via electrical impulses.
Ultimately everything Jane has ever seen, heard, touched, smelled or tasted has only been in the form of an electrical impulse(s) that has travelled from Jane’s external surface or her internals via her sensory apparatus (eyes, ears, etc.) to her brain where those impulses are somehow via some sort of electro-chemical wizardry perceived as being something Jane identifies as, for example, Clive. Jane has seen (reality once removed) photons reflecting off of Clive that have entered her eye and (reality now twice removed) converted into electrical impulses which the brain (reality thrice removed) processes resulting in an image, sound or other experience that resides 100% inside, and only inside of Jane’s brain. What is perceived inside Jane’s brain is only a simulation of Jane’s external reality, part of which is Clive. By a similar form of reasoning, Jane has never ever seen the true really real version of her own self! As an aside, this might imply that distance or depth is really an illusion**.
Jane never experiences Clive directly, only indirectly. If Clive can only be perceived indirectly (reality several times removed), then maybe there is no Clive since Jane cannot prove even to herself that Clive really exists and thus Clive might be a total figment of Jane’s mind and imagination.
One other point needs noting here. If your brain accepted and processed all of the experiences you could be experiencing, you’d go nuts (that’s a medical term)! You are bombarded with way more stimuli than your brain can cope with. The brain has to filter out most of what it’s bombarded with, probably by eliminating much of the duplication. So for example, if one billion light photons reflect off of my cat and enter my eye every second, then my brain might process only one thousands of those photons, but that’s enough for me to ‘see’ my cat. At least I hope that’s what’s happening otherwise there might be aspects to my visual cat that I’ve never experienced.
It does seem a sort of paradox by the way that we ‘see’ what the brain / mind perceives after all of those photons, electrical impulses and electro-chemical wizardry have done their thing, even though the mind / brain is in total pitch-black inky darkness.