“It seems to me that S&M is about two things: being brave enough to play with power and realize it’s moveable and malleable, and also the deire to be overwhelmed and to be overwhelming. Which is no different than any other kind of sex if it’s any good.”
-Maggie Gyllenhaal, 2002 as quoted in “Nerve: The First Ten Years“
To me, the creative interplay between power and affection is what defines S&M at its best. Some use that interplay to twist power and affection; others use it to untwist them.
As to being overwhelmed or overwhelming, that's mostly in the mind's eye. And that's where some of the most memorable sex happens.