[...] Please do not on any account let yourself be misled by my mistake in casting the better artiste for the part of Kurwenal! I have paid for my error heavily enough already, for it has been perpetuated, and neglect in the casting of Mark has reduced this important rôle to ineffectiveness, so that the force of the whole of the second act and of the greater part of the third act has been lost. The parts in the order of their importance may be set out as follows:
I. Tristan—Isolde—Mark
II. Kurwenal—Brangäne—Melot
Only believe me and have a good look at Mark—yes, only read through his part!—Well, it does not look to me as though anything would really come of Tristan in Berlin this winter! It is a hard and difficult enterprise, my lads, and demands long and ardent wooing! If only you remain faithful and true to me! I need a few good men, for I have difficulties, anxieties, troubles and worries enough and to spare! [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 678