Akinbo
I am not bothered who else said this. It is a fact, that is how, generically, the physical existence we know must occur.
Now, you raise the right question, but it is not a challenge, it is very easy to explain. Well, generically anyway (as per my essay). How this actually manifests in our existence is very difficult to establish, and that is what physics is supposed to be doing.
Based on the physical input we (and all sentient organisms) receive, we know that that form of existence has two fundamental characteristics;
-what occurs (ie exists), does so independently of the mechanisms which detect it
-it involves difference, ie comparison of these inputs reveals that there is difference, and therefore alteration.
Hence the apparent conundrum (or illusion as you say). On the one hand for existence to occur there must be something definitive. But on the other hand, we experience change thereof. The resolution of this lies in a proper understanding of sequence, and the abandonment of the incorrect ontological concept of 'it changes'. A difference is a difference, not the same with a change, which is physical nonsense.
So the existence we can know is existential sequence. Whatever comprises it can only exist in that sequence in one discrete, definitive, physically existent state at a time, the predecessor must cease to exist so that the successor can exist, and so on. That last phrase is critical, and physically correct, but is the opposite from how we fundamentally conceive of reality, with 'things' and 'changes'. Whilst it is obviously important to understand what comprises reality, substantively, and causes difference, the concept of physically existent state is crucial. Things do not exist, a physically existent state does.
To put this simply. Take any thing around you. There is a cup of coffee here. Now, that appears to be an existent thing. But we know that if we wait long enough, we will see alteration. We know that if we put this under an electron microscope, we will see alteration. And we know if we could subject it to a more detailed examination, we would see more alteration. In other words, the question becomes, when is that cup of coffee a cup of coffee. And the answer is never, or once, depending on how one wants to phrase what is actually happening.
From one point in time to the next it is not the same. What is happening here is that we are conceptualising physical existence (reality) from a higher level than that at which it occurs, physically, via certain superficial physical attributes, which are not actually existent. And we deem this 'thing' to remain in existence whilst those attributes pertain. Indeed, we then rationalise alteration by conceiving that it has changed, which, physically, is nonsense, because if there has been alteration then something else exists.
In sum, there is no 'cup of coffee'. It is, physically, a sequence of occurrences, one at a time, which bear a superficial resemblance. These occurrences being the physically existent state of whatever is involved. Each of those states being a reality. That is, there is no degree of alteration within a reality. That alteration is what differentiates one reality from another in the sequence, ie one physically existent state from another.
Paul