Norms erode internally before behavior changes

Norms and conventions are very stable because if everyone adheres, payoff forces push everyone to keep adhering, but a norm can be eroded—people can become dissatisfied with it and come to believe it unjust—well before any behavior actually changes; real change requires someone to actually act differently (the disadvantaged making higher demands and disrupting things, or the advantaged conceding more), and the disruptive route is observed more often than voluntary concession.