I think for myself, it started in 3rd grade. I was trying to get closer to my very first crush. I soon found out she took karate classes at a nearby dojo. I convinced my parents to let me join and a week later i was on my way to maybe being able to finally talk to her. There was one crucial thing i didnt factor into this equation. She was already a green belt, number 5 out of 10 belts to move through. The owners of the place wouldnt let you spar or fight someone more then 2 belts higer then you and i was on number 1. So hense i watched from afar as she trained and fought with all the higher ranked kids on the other side of the building, dreaming of when i could go and have a chance to get my ass beat just to have a chance to get to know her. Nothing ever came of me and martial arts past novice level and soon i was moving on to baseball, but that stuck with me because years later in 6th grade, that ended up as my first sexual fantasy. Her in a towel kicking my ass and bam, instant turn on. The idea of getting hit in the balls left the biggest impact. I guess just with it being such a sexual area. I was amazed to find porn for such a thing around age 15 or 16 thinking i must have been the only one into it, but alas, how wrong i was. I didnt truly embrace my full inner BDSM self until i was 18 when i lost my virginity and started my first long term relationship. After about a year we both revealed our strangest inner fantasies and it turned out we were both into being submissive and took turns. I never really felt fulfilled though. Neither of us could truly pull off being dominant. The fortress helped fix that in a hurry