Anticipation can be a big part of play. I love the idea of knowing what's going to happen (at least, to some degree) and having to wait for days, maybe even weeks or longer if you're meeting someone from further away.
In my experience the reality usually surpasses the fantasy. I'll remember the rush I got from a painful scene, and I'll imagine myself much braver than I end up being in the face of the real pain. A good top will not let me off easy, and will push me through to the place I need to be -- and that means it is going to really hurt. It is hard to go through.
A trepidation rises up right before meeting someone. I always tell myself to try not to think about what's going to happen, and that "whatever he gives you, you will take -- and you will survive." ("Survive" used rather loosely, depending upon the condition of your bottom.)
When I lived and worked in South Jersey, I used to play with a dom who lived a little north of Philly. That meant leaving work on time (not always possible) and dealing with the traffic on I-95. Even if I left on time, inevitably I'd be watching the clock in the car, nervousness increasing as it became more and more obvious that I wouldn't make it there on time.
This particular dom was VERY intense and scary. He'd beat me hard, late or not, so my anxiety was legitimate. Truth was, deep down he was a "normal," caring, real person, so he always understood when I was late and never really got angry. He simply used it as an excuse to give me more of what I already needed.
But oh, the dread I always felt sitting in that car, the tingling, pulsing, fear-induced excitement that sent hot waves through me ...
These days I feel so jaded, compared to my relative innocence and newness back then. He was one of the first tops I'd played with who wasn't a boyfriend, and I was just beginning my serious exploration of the scene.
Now I don't have as many nervous butterflies. Sometimes they stay hidden away until the moment I walk in and see an implement that I hadn't expected. Then it suddenly hits me: "Oh, shit, this is going to hurt!"