To be fair, in many cases, the observable behaviour of things is different at scale. A single water molecule has different properties to a cup of water, in much the same way that a high density crowd of people (greater than 4 people per square meter) starts to behave as a fluid.
I study biochemistry and I'll never stop finding it neat how when you get down to the teensy tiny level, all the rules change. That's basically what quantum physics is, a different ruleset which is always "true", so to speak, but it's only relevant when you're at the nano scale
I suppose what I'm saying is that I agree with you, that fathoming scope is difficult, but I'm suggesting that this is a property of the world inherently getting being a bit fucky at different scales, rather than a problem with human perception.
It's a term from gaming which, in the broadest sense, means how they paint the sky to make it look authentic. Imagine being inside a cardboard box - the sides are painted to look like rolling mountains and hills, and the top face is painted to look like a cloudy sky, and if it's done well, all of these should connect up and give the impression that you're lookint at a real sky.