I watched on ARTS a short selection from an interview of Waltraud Meier talking about her career as the perpetual Kundry at Bayreuth. She spoke of working the role with James Levine, Riccardo Muti and Daniel Barenboim. "These are three different worlds." Then she asks "what is music?" It is nothing definite. It is life. It is something that changes as life changes. It is personal, individual expression.
That's as close as I can get.
It is vitally important to note that she got this gig by simply calling them up herself and auditioning. She had just finished doing Kundry at another house where she worked with Jean-Pierre Ponnelle, the director and designer.