This is a hard concept to grasp. I think the answer is that we usually try to explain things in physics by relating it to something we have experience of. We know what a particle should look like … like a solid ball of matter. We also know what a wave should look like because we see them on the ocean.
Probably, very very small things like electrons can’t really be compared directly to balls or waves on the ocean…. even though they have some properties of both of those things. If we could ‘see’ electrons… which we can’t (seeing something is just bouncing light off it) .. they probably wouldn’t look like anything we’ve seen before.
I wish I could!!!!! I just go with it. When I use different wavelengths of light for spectroscopic analysis in the infra-red region it behaves like a wave, when I use it in teh ultra-violet region it behaves like a stream of particles. It baffles me to this day!!