NB: This is not triggered by issues in any of my relationships. Mostly, this comes from a) having just finished a book on power politics, and b) being madly caffinated at 4:23 am. I am willing to discuss why I am wrong, in this thought.
Editted to add - the only power someone has over you, then, besides the power to leave, is the power you *give* them. This exchange is made explicit in D/s relationships, but I think it applies to *all* relationships.