Complex sentence: The reason Nietzsche sees this as contemptible is because he sees suffering as necessary for cultivating human excellence, for example in The Gay Science, where he writes: "Only great pain is the ultimate liberator of the spirit" (GS pref: 3).
Split into simpler sentences: The reason Nietzsche sees this as contemptible is because he sees suffering as necessary for cultivating human excellence. Thus in The Gay Science he says: "Only great pain is the ultimate liberator of the spirit" (GS pref: 3).