Curiosity of a straight guy

As the title suggests, I'm straight. But I am curious about something. See my wife and I are rather open to each other sexually, as in we've done almost everything we can think of, and I got curious one day after she wanted to try anal. We did it and she liked it and all since she likes a hint of pain and what not, and since I get random thoughts all the time, I wonder, when you have sex with a partner, is it a mix of pleasure, pain, or both? Like what exactly appeals about reviving? Sorry if I bother anyone with this question, just super curious about what provides pleasure in that situation. Thanks!