I have often asked myself whether I am not more heavily obligated to the hardest years of my life than to any others. As my inmost nature teaches me, whatever is necessary as seen from the heights and in the sense of a great economy—is also the useful par excellence: one should not only bear it, one should love it. Amor fati: that is my inmost nature. And as for my long sickness, do I not owe it indiscernibly more than I owe to my health? I owe it a higher health—one which is made stronger by whatever does not kill it. I also owe my philosophy to it. Only great pain is the ultimate liberator of the spirit, as the teacher of great suspicion which turns every U into an X, a real, genuine X, that is, the letter before the penultimate one. Only great pain, that long, slow pain in which we are burned with green wood, as it were—pain which takes its time only this forces us philosophers to descend into our ultimate depths and to put away all trust, all good-naturedness, all that would veil, all mildness, all that is medium things in which formerly we may have found our humanity. I doubt that such a pain makes us "better," but I know that it makes us more profound.

Nietzsche contra Wagner
"Out of the Files of a Psychologist"
Epilogue, 1