quoted from "Quantum Mechanics: Non-relativistic Theory" by L.D. Landau, et al, page 2, Pergamon, 1977

"In quantum mechanics there is no such concept as the path of a particle."

This is supposed to form the full content of what we now called the uncertainty principle. This also gives a reasonable explanation for the double-slit experiment or electron diffraction experiment.

But for low speed of classical physics, path of a particle is an observable that is capable of being verified by experimentation.