Why men and women can't be friends

Oh did I get your attention with that title? I hope so, but let me explain myself. I'ts not to say that men and women don't have the capacity to be friends, I merely think that we are not able to be close friends without complications. This is something that I have only recently figured out, and my observations are my personal opinion so take it with a pinch of salt. This is what I like to call the 'When Harry met Sally' theory.