True enough CH, but let me contend that one reason I like my D/s relationship (which isn't, per se, a 24/7 power exchange,) is that when I want to bend her over to fuck her, I do. Tired just doesn't matter. Mood is irrelevant.

Now perhaps this works for me (and them,) because I choose submissives who are genuinely stimulated by being "of service" and being used regardless of their momentary feelings. It stimulates something deep within them that they are loved and cherished and needed. It's why they give up their power to me.