Individual anger at mistreatment stays private until someone organizes it, leads it, and aims it at one specific goal. Then it can become a mass movement. A personal insult from a bus driver became a citywide refusal to ride once ordinary riders were persuaded to use their fares as financial pressure.
Where a system treats some groups as more threatening than others, the less-feared group can protest more openly. Black women saw that the racial and gender rules of their society made them seem less dangerous than Black men, so they had more room to step forward.
Constant humiliation wears down a group's self-respect, and that damage can show up as crime and violence within the group, including at home. Organized community action for rights can reduce both the humiliation and the harm people do to one another.
A famous act of defiance can launch a mass protest overnight only if an organized group has already planned for it. The group that had prepared the boycott well in advance was able to start it the very evening of the arrest. The public story then remembers the spark and the spokesman, not the people who laid the fuel.
An institution that depends on hostile authorities can still back a movement, but only by keeping its part hidden. The city's only Black public college quietly supported the boycott while keeping a low public profile to protect itself.