An act of positively focusing is to separate something from the whole.
It creates separation (in our mind, or in the system where focusing occurs), and this separated part of the world becomes the virtual world as long as the focus is maintained and the rest of the world is forgotten/ignored and recedes into background as “negative area”.
Usually, our focus changes, and this virtual world retains the sense of temporal, virtual, relative nature, especially when the focusing is done with full awareness of criteria for separating focused (positive) zone and background (negative) zone.
However, we seem to have natural tendency to consider certain focus as if its absolute and to hold it nearly constantly/permanently. ( The problem of sticky focus)
In this state of narrowed vision, the person would consider the virtualized and partial world as the real and whole world.
I’d say, this is the nature of most beliefs in many of us.
Also, it is interesting to note that the separation is done by selective admission of certain things while denying others.
It is similar to any other “container”, “cell”, “bag”, etc.
The division/membrane separate inside from outside by selectively permitting/denying the passage.
And the separation seems to be always “virtual”.
As far as I’ve thought about, I haven’t seen any absolute isolation/separation.
A fish tank can separate small space in our room to create virtual world for fish, or whatever we put in.
But the separation isn’t total. Usually the top is open to the air and we can put our finger from the top, and fish can bite. 
Also, the virtual world is restricted by the separator, and it’s relative to the existence and the nature of the separator.
When the separator (often glass or plastic in this case) breaks, the virtual world may cease to exist, too.
As far as I’ve observed, what we may call “ego” is a sort of virtual world. Also, our surface consciousness and subconscious region are separated in the same way, by positive focusing and negative background.
There are many people who love to see just “positive” things. The very act of clinging to the positive things would separate the whole world and creates another layer of virtual world and huge chunk of negative underworld.
When our perspective is relatively free, we have possibility of seeing our subconscious region and things we may not like to see.
Usually, it’s not the case, and most of us would stay ignorant of lots of things.
We have natural tendency to focus on things.
By desire, curiosity, interest, etc, we would focus and magnify certain thing.
As we grow up, some of us would feel strange about the limitation, contradiction, negative feeling, etc, and start to question.
And the act of questioning may lead us to think more logically and examine our world (world view/perspectives).
Depending on the nature of the each person and the environment, some of us would continue to question and break away from some fixations (beliefs).
But so many others would collide against the “virtual glass wall”, get scared or uncomfortable feeling, and eventually decide to stop questioning. When this “denial of questioning” happens, it’s usually done by adopting new self-imposed restriction or by enhancing existing separator(s).
Children are innocently trapped in certain virtual world, while some adults have willingly placed themselves in the restrictive space. It means their virtual world has one more layer of separation and thus harder to break, even if they wished so, later.
Religion, ideology, social and economic theory, nationalism, and so on are all products of virtualization and illusion based marketing.
It’s done by glorifying and magnifying certain aspects and overrate then while denying other things.
And finally, so called “existence” might well be yet another virtual layer we tend to believe so much.