Patton Oswalt has a decent bit called "Piss Drinkers." (If you feel like it, you can find it here.) In a nutshell, the idea is if you can think of something, it's a fetish.
Like most things related to the way humans interact with each other (I swear, I am not a secret cyborg), kink/BDSM/fetish is neat to learn and know about. I knew going into the whole awkward hormonal teenage stage that I didn't really like monogamy and what it represented. I also knew (although denied and tried to explain away for a few more years) that there was something particularly about other ladies that was completely fascinating in a tingly sort of way.
I've come across people sometimes in the kink lifestyle who can describe their interest in BDSM the same way - they just sort of knew. It wasn't like that for me. When I was busy making out with some select other drama crew members (yes, I was that kid in high school - marching band was bereft of ladyboner material, also weirdly full of couples - go figure), I wasn't ever thinking how awesome it would be if we could also tie each other up, or if one of them would just slap me around a little bit.
I had a girlfriend for awhile in college who was also a Domme. I didn't know this going in, but I did know that I liked having sex with her. So when she brought up the idea of handcuffing me to a ring hooked in the ceiling while she fucked me, I was game. I want to really clarify that it wasn't anything where I thought I had to in order to make her happy, or that I did something I was fundamentally uncomfortable with just to somehow keep the relationship going. It was more of an, "okay, we can do that" shoulder shrug and then I wound up really liking it.