Maybe it's years of experience, but I get it... I can't think of any that I don't. There's plenty that I'm not into, but I'm hard pressed to come up with any that I don't understand. I'm sure someone could stump me, but I can explain nearly any. Of course, with any particular fetish, there's plenty of different reasons people might be into one; but often there's a "most common reason" vs more random ones.
For example, I have a fetish for having my significant other cheat on me with men. People come up with all sorts of reasons, but I have my own theory which is very obvious to me but not to the people that don't know my history... right when I was hitting puberty, my [crazy] mother would come up with all sorts of horror stories about how my father was cheating on her with men. I sexualized it somehow, and now it's nearly impossible for me to have an orgasm without watching my lover with another man or at least imagining it. It's a blessing and a curse.
