Nietzsche wasn't simply saying that suffering builds character—a platitude we've all heard. Rather, he was making a biological and psychological claim: that organisms genuinely *transform* through resistance, becoming fundamentally different creatures, not merely tougher versions of their former selves. A musician who struggles through years of technical failure doesn't just develop perseverance; her ear, muscle memory, and creative instincts are rewired by that very struggle, making her literally incapable of playing the way she would have had success come easily. The quote's real power lies in insisting that difficulty isn't something we overcome and leave behind—it's the material from which we're actually built.