In my opinion, the wave-particle duality is a very useful tool in quantum mechanics if used correctly, which is what I will attempt to explain in this post. As noted many times in this thread, the wave-particle duality is incorrect if we are talking about what the particle “is” as a quantum particle is not classical in any way. Describing a quantum particle as “being” a combination of two classical things, i.e. a classical wave and a classical particle, is thus completely incorrect. We logically, of course, name these things “particles” seemingly in an attempt to confuse people trying to learn physics (as has been noted many times, this name is a historical mistake).
What, I would argue, should keep this wave-particle duality notion around is when talking about properties. We can connect many properties of a quantum particle to classical particles or to classical waves. Note that these are just merely analogies to allow us to wrap our heads around quantum mechanics. It is true that quantum particles share many properties with different classical objects, but this is not to say that are a combination of those objects. Sometimes, though, depending on the problem we are trying to solve, the wave-like properties or the particle-like will become very important, to the point that mathematically, we can treat it much like one of those classical particles. This, again, is not to say it is one or the other at that time, just that in our problem or experimental setup, we are trying to bring out one of these properties. The quantum particle still retains all of its quantum properties, and does not “become” either a particle or a wave, it merely acts like it because we are, in a way, manipulating it to do that. Still, in no way, is it a classical ball bouncing around everywhere, or a classical wave (though it may act like it). Hopefully you understand here that we are not talking about what it is, but what it acts like in certain situations.
This kind of labeling, unfortunately, appears more than once in quantum mechanics. For example, we like to say that an electron has something called spin. Though, in a way, the electron acts as though it is a little spinning ball, very few people actually think the electron is spinning like the Earth. This is, again, a historical mistake. Although, I should point out, we can’t say for sure that it’s not really spinning, just that we don’t think it is. Naturally, we label that property as spin ;).
