According to Cialdini's principles of influence, what psychological trigger underlies the 'scarcity' principle?

According to Robert Cialdini's principles of influence, the primary psychological trigger underlying the 'scarcity' principle is 'loss aversion,' combined with the 'reactance theory.' Loss aversion, as a cognitive bias, suggests that the pain of losing something is psychologically more powerful than the pleasure of gaining something of equal value. Scarcity exploits this b....