My two cents:
In my real-life experience, I spent my late teenage years through my twenties as a dedicated masochist (but not a sub, oddly). I had a long-term partner who shared this inclination, and we alternated roles, taking turns in exploring the bounds of pain. While this technically made us switches, our primary focus was on experiencing pain rather than adopting a sadistic persona. Naturally, over time, we evolved into those roles. What began as simple spanking games gradually escalated into very hard CBT-electro sessions with predefined minimum intensities and durations. Our deep understanding and trust in each other made this progression feasible and natural. However, I have never achieved this level of connection with anyone else since. Inflicting such pain is not a trivial pursuit; it requires complete trust, even knowing the experience will be intensely painful - tears, screaming, the whole lot. Our motivation was simply to see the other endure suffering or to experience it ourselves—essentially, torture for torture's sake.
Interestingly, intense pain doesn’t really turn me on. A little does, but not the level I used to endure—it genuinely hurt. I cried often during those sessions, as did my partner (when it was his turn), and I frequently regretted my choices early on. I’ve always found it amusing how torture is often depicted with men having raging erections. In my experience, when they’re crying and begging for the pain to stop, what most men actually have is something more like a gnocchi-sized thingy between their legs. And yet, the memory of having endured all that pain turned me on more than anything else. Literally, more than anything. I’ve thought about this a lot, and my best guess is that it’s similar to the thrill of extreme sports. What do you think?
In the stories I'm writing, the protagonist switches roles for reasons I don't want to spoil just yet. As a writer, I wanted to explore having both a man and a woman "on the rack," and since I prefer writing in the first person, this required me to change both roles and perspectives. Their motivations are quite straightforward and mundane: sadism and masochism.