> Yes but AFAIK, reality is "quantum" in the sense that something like the scale of Avogadro's number (N=10^23) quantum processes interact and average out to typical classical behavior. It's only in limited situations where the actual quantum mechanical nature pops up in the macro world, right? (eg Bose-Einstein condensate, the ultraviolet catastrophe, energy bands of semiconductors, emission spectra, etc).
This is not very clear at the moment. Of course, observations make it obvious that classical objects don't behave like quantum objects, and all quantum objects we know of are small, and all classical objects are big.
We even know of one mechanism that prevents certain quantum effects from influencing large systems - decoherence. Decoherence explains why, when a quantum system that is all in the same phase interacts with a large system where everything is out of phase, the various parts of the quantum system also quickly go out of phase, and thus can't constructively or destructively interfere with each other any more. This explains for example why, if you repeat the double-slit experiment with ping pong balls instead of atoms, or if you repeat it in a dense gas at high temperature, you won't see the interference patterns form.
However, we don't understand at a high level why it is that quantum experiments only have "a single result". Basically the schrodinger equation applied for the double slit experiment, even taking decoherence into account, still predicts that the particle-wave will move through both slits to some extent. And yet, with or without decoherence, we only ever see a single photon or tennis ball hit the screen, with some probability that can be deduced from the square of the amplitude of the Schrodinger function. And even worse, this single measurement outcome only happens if the quantum particle has hit a classical screen. If instead at the same distance we only have other quantum particles, then it can actually hit several of them, and change all of their positions and momenta. This despite the fact that, of course, even the classical wall itself is made of particles which should obey the same laws of quantum mechanics.