Many scientists have their theories about what's going on in that box...Is that cat dead or alive? Is that radioactive element decayed or undecayed? The answer is simple: We don't know. We can never know unless we open that box and opening that box would just kill the purpose of that experiment. The theory that stands out is that the The cat is both dead and alive at the same time . It's as if the nature didn't make a decision yet. The radioactive material is also both decayed and undecayed at the same time. And the moment someone opens that box, nature takes split decision and the cat goes from an intermediate state to an absolute state. Either it becomes fully dead or fully alive.
This experiment also explains the observer effect. The presence of an oberver to that experiment can completely change the outcome, just like the cat went from being in intermediate state to alive or maybe dead.

And no, the phenomenon is not only limited to the cat, It happens all around us...it is a very common happening in microscopic particles. And I know it hurts the brain to visualize how exactly that works. This is because we are born in a macroscopic world, we understand things as they happen in large objects. While superposition is a property of the world of quantum physics, including electrons, protons, atoms...what and what not.

It is not yet possible to achieve this state in macroscopic world but scientists are currently working on it to make this amazing phenomenon happen in our world too, only then we can experience how it feels like to be in two states at the same time