Why do atoms interact differently? We live in a 3-dimensional Universe, so why don't atoms (electrons) follow the same rules as humans, planets and other 3-dimensional objects? So does that mean electrons and other quantum objects pop into existence from another universe or dimension?
 A: You think you are observing “classical physics” when you observe humans and planets, but what you are actually observing is the classical limit of quantum physics. Quantum physics applies to humans and planets as well as to electrons and atoms, but what we think of as quantum effects are not noticeable for large objects.
There are no special rules for small objects vs. large objects. The rules just appear to simplify for large objects, as an excellent approximation.
Electrons are not popping in from another universe or dimension. All objects are believed to play by the same quantum rules. This is why physicists are trying to understand the quantum mechanics of black holes.
A: The pursuit of knowledge is the asking of many questions. The question you have asked here is a complex one, about which whole books have been written, but I will try to give you a brief answer. 
The quantum rules that govern the behavior of objects as small or smaller than individual atoms are quite different from the classical ones that govern the behavior of objects the size of baseballs, humans, and planets. 
Nobody asked for this to be true, but inescapable evidence in support of this basic truth was firmly in hand almost 120 years ago, and required the replacement of classical rules with quantum ones, which were derived mathematically and then proven to furnish a satisfactory accounting for what goes on in the world of the ultra-small. 
As you study the behavior of increasingly large objects, the quantum rules reduce to the classical ones. 
