In quantum world things are routinely in multiple states at once - what we call a “superposition” of states. But in the classical world of large scales, things are either this or that. The famous thought experiment is Schrodinger’s cat - in which a cat is in an opaque box with a vial of deadly poison that’s released on the radioactive decay of an atom. Quantum mechanics tells us that the atom’s wavefunction can be in a superposition of states - simultaneously decayed or not decayed. So is the cat’s wavefunction also in a superposition of both dead and alive.
