I'm asking this question not because of my own misgivings but someone else on this forum some time ago made a comment in a different context which, when talking about teaching Quantum Mechanics, was something like, "Do they still teach things like the particle-wave duality, too?" as a criticism. I simply don't know enough about this other than a rudimentary understanding and vague relation to the De Broglie wavelength and the Photoelectric effect, and haven't run into it as a standalone topic in QM. I'd like others' thoughts on this, because as far as I am aware with my pretty limited knowledge, particle-wave duality isn't some ridiculous, fundamentally flawed concept as the poster made it out to be. Even if it was, I still think it was a little absurd that the above was said when we still teach things like the plum pudding model as a temporary stepping stone to an electron cloud model, or we still teach the octet rule in Chemistry despite it only being valid for very limited cases; particle-wave duality could, carefully applied, be a pedagogical tool, regardless of if it is exactly true. What is (or is not) wrong with particle-wave duality?