From what I understand, QM is all about uncertainty. The wavefunction (or rather $|\Psi|^2$) gives us a probability of finding a particle at a certain point. Then, we measure the particle, and find what point it is at.
Now, here's my trouble - QM states that before we measured this particle, it was in a superposition of many states and did not have a definite position. This also implies the wave function is "perfect" because it gives as accurate information as possible about the position particle before we measure it.
So, how do we know this? Why can't there be a function $\phi$ that doesn't give probability distributions, but instead gives definite locations of particles, and we just haven't found a way of expressing or computing it? Why do we know that the position of particles is physically uncertain, and not just unknown to the experimenter? Sure, Quantum Mechanics works out beautifully and fits the results, but perhaps it is simply a very good theory of probability when we have a much more elegant and simple theory?