Yeah, I'm going on about wave particle duality again

I started reading 'the universe in a nutshell' last night and I decided to do it properly, I mean with a textbook and exercise book by my side and everything! So I went off on a bit of a wave particle duality tangent and suddenly it clicked. Like I never really liked the idea of a photon as a particle because it doesn't have mass but then I realised, energy and mass are equivalent! It seems obvious now... Its just how you look at it. I still can't visualize but its just a concept....