Full Idea
Fear has furthered the universal knowledge of humanity more than love, for fear wants to discern who the other person is, what he can do and what he wants.
Gist of Idea
Fear reveals the natures of other people much more clearly than love does
Source
Friedrich Nietzsche (Dawn (Daybreak) [1881], 309)
Book Reference
Nietzsche,Friedrich: 'Dawn (Daybreak) (v 5)', ed/tr. Smith, Brittain [Stanford 2011], p.191
A Reaction
Nietzsche had it in for love at this stage in his career. This remark strikes me as brilliantly accurate.