That could be true.
Or maybe he only reffers to himself, only he phrased it wrong. Like Descartes, he questions himself and his existance and the only thing that is concrete to him is that he thinks. By his reasoning, thinking is the only proof he has that he exists.
It's basically like saying you don't know if you're in a dream or awake and if all you know is just an illusion. Mayb in 2 seconds you're gonna wake up and all you know will have been fake but the fact that you thought it makes you be.
Afterwards, you can argue that there is no way that this is a dream because dreams can not be as complex as this. But hen again if it is a dream, then how would you know for sure?
By this logic you can prove that anything is real to you, not to others because you don't know that others think. To me, an atheist, this is the most interesting part of religion: They are a group of people who know that everyone belonging in their group thinks. That's what makes all the surrealistics beliefs like wine turning to water etc. possible.

I say all this but I haven't studied philosophy in any way. Maybe my interpretation of Descartes is completely wrong ; if there is such a thing as wrong in an interpretation.

Also, I realise I'm a little off topic at the end.

If everything is an illusion then the only practical knowledge is to know how the illusion works. If it obeys consistent rules, then the fact that it doesn't exist is irrelevant. Its stimuli exist, and that is the base upon which we make our future decisions.

Indeed.
And I think the initial question was, What would happen if we don't seek the knowledge of how the illusion works?
And there I agree with Megadoomer:

So it won't happen and the next question is: What if it could?
If the world is concreet as we conventionally think it, then nothing would happen.
If it's an illusion, then the infinity of possibilities of how the illusion works would make the result unpredictable. You could "dissapear" as suggested in the first post, you could discover that you're bald and are providing energy to a machine ruled world (Matrix) etc.

I have to lol at all the people who simply dismissed the original comment in this thread. While it was poorly worded, it had a very good point behind it.

For similar ideas you only need to read Descartes' Discourse on the Method and the thought experiment of Schrіdinger's cat.

But even if this was the way things are, in doesn't really mean anything. How can you not think about your own existence? Merely by experiencing your own 'existence' you are thinking about it in some way. So if this is true it really does amount to nothing.

The closest thing to non-existence that we have experienced is sleep.

I struggled with the same thing as a kid...

I just realised that there is no reason not to take everything as it appears, as that just causes paranoia and anxiety (see: my childhood) so far is hasn't let me down. :P

I thinked about that very much in my early ages. That took me a while to fully undarstand the meanings of non-existence, begining and time.

I think the closest anyone is going to get to be non-existing if you get knocked the fuck-out and that is different then when you are sleeping because you are going over experiences in your head and working them out. You are really never non-existing unless you actually don't dream at all and the pineal gland is obsolete which would probably mean you are dead. You are always dreaming when sleeping in which ever cycle and your brain is more active during R.E.M sleep. You just don't remember them, but subconsciously you do.

If we all lived alone 99% of our life would we be alive or would it be a bland world of no life like all the other planets in our soler system. well if were just alone with out any social conflicts then we would all die out from the lack of reproduction.. so i guess with out social life, life wouldn't exist would it?
Is all matter in existence? or are we always gonna ask these questions and never find an answer?