One of the directors on Raffish's recent selection of DiD scenes with commentaries from actors and directors involved in the scenes said that he thought that the interest in bondage arises from an infantile need to assure an adequate supply of breast milk.
I don't agree with that analysis, it's just way too pat for me. My theory is "I don't know." I've yet to hear a convincing explanation for the bondage fetish, and I've read a lot of them. But I do know that this is an excellent opportunity to show the pic above of Darling's very fine natural left breast in bondage.
Provenance unknown, but that's Darling's breast, alrighty.