You're not getting away with this lazy shit. This is a philosophy forum so define your fucking terms, man.
Why do you choose the word 'world'? Do you mean separate states of existence, something physically tangible, a particular configuration of neurones? What?
Well, at least you're asking now instead of projecting. Even if it's not exactly polite...
What i mean is that we spend our entire time in either one of those worlds. We either accept what is happening to us in our lives, or we try and reject it, or change it. The accepting mode is the World of Is, the trying to change it mode is the World of Should Be, because that's what we think something should be. We don't like something, so we try and change it. Now, if we can convert what we see as wrong into what we see is right, then fine, perhaps it's worth going for the change.
But if we can't change what we see as bad, then it's better for our health to accept it.
Of course, we will need to have a reasonable grasp of what we could change so that we know it's worthwhile fighting.
But anyone who's fought something because they think it's wrong, but could not change one thing about it, will have experienced the angst within their bodies from the failed fight.
So, rather than simply inhabit the ideal world (which you initially presumed i was saying), ie the world of is, my idea is to better know oneself the fights in life one can get a win of some sort, and to better know the fights one can never win. Accept the shit if you can't change it. Fight it if you think you can.
It's a balancing act either way.