Capitalism is fundamentally invested in notions of scarcity, encouraging people to feel that we never have enough so that we will act out of greed and hording and focus on accumulation. Indeed, the romance myth is focused on scarcity: There is only one person out there for you!!! You need to find someone to marry before you get too old!!!! The sexual exclusivity rule is focused on scarcity, too: Each person only has a certain amount of attention or attraction or love or interest, and if any of it goes to someone besides their partner their partner must lose out.