Conan the Nietzschean… Way to go, Conan.

The quote is taken from Twilight of the Idols (Die Götzen-Dämmerung, 1895). It’s the 8th maxim from the section “Maxims and arrows” (the very first section of the book, after the preface). Here is a slightly different translation : “Out of life’s school of war: What does not destroy me, makes me stronger.” (tr. by Walter Kaufmann and R.J. Hollingdale here).