[...] The manner in which I create my dramatic works, whereby I write not only the music but the entire musical drama, is now so much second nature to me that not only could I no longer reconcile myself to the idea of setting another writer’s dramatic poem to music but I recognize that this must be my most important goal in the future - & one which I ought to be capable of achieving. I am now fully convinced that if anything of significance & validity for the history of art is to emerge from this particular genre (which I see as diametrically opposed to the “opera industry” of the present day), this can only be so if the poet and musician are one & the same person. By following the old dispensation you will at best produce a decent libretto or decent music, but never a genuine musical drama, indeed I shall never be able to understand how two artists could ever create a single work of art. The fact that I have grasped a subject which came to me alone, that I elaborate it in such a way that I myself can no longer say which parts show the influence of the poet & which the influence of the musician, and that I finally complete both words and music just as the subject originally appeared to me in vague outline - all this I find adequate justification for my exclusively creative - and more especially my musically creative powers. In addition to which I am always so richly provided for with future ideas that, given the tedious waste of time involved in completing an opera, I am afraid that I shall carry with me to the grave a number of ideas which I have not had the time to elaborate.
[...]
Source: Selected Letters of Richard Wagner, trans. and ed. Stewart Spencer and Barry Millington (W. W. Norton & Company, 1988), No. 69