This question already has an answer here:
So...if electrons and photons are both particles and they pass the two slits, why do they create an interference pattern as if they were waves? Now from what I've read, it's because of the superposition of an electron and since an electron is in every possible state until observed, it is going through both slits and interferes with itself and that's why, if not observed, the double slit experiment will show that interference pattern.
Now my question is: how can that electron propagate as a wave if it interferes with itself? Shouldn't the outcome of the experiment be the same with or without an observer? I mean...that's just so very extremely counter-intuitive that I can't grasp it...an observation changing the outcome. Why does the observation of the slits change the outcome and not the observation of the screen? Why do we get wave interference even with one slit?
Please correct me if I'm mistaken about how this double slit experiment works cause I've also seen interpretations about the wave nature of electrons and photons and it just made things more complicated for me.