It has nothing to do with a person's own self worth, for some of the Worlds most powerful and confadent men and women are subs behind closed doors.
I can only really speak for myself here, but there is just some part of me that craves having no control about that particular facit of my life. I don't want to be a full time slave. I want to have an equal partnership when it comes to Money, or raising the kids, or work, or anything other then sex.
But when it comes to Sex, I want my Mistress to be in control, and want her to know what she wants, when she wants it. I want her to demand perfection, and know just how to push my buttons to push me to perfection. I want to feel the leather bonds, preventing me from escaping, but also knowning that the bonds are meaningless, for it is not the leather, but her mind and soul that holds me still. I want her to bring me to my limits, and help me find a way to surpass them. I want to know that I can trust her with this control over me, for I know that with either a word or a gusture I can end it if we have gone too far or too fast.
Of course, not everyone is like me, so others will see this as a weakness, but to me it's coming home.