When it comes to helping people, a known principle in human psychology is the bystander effect. According to it's principles, the larger the number of people who witness an emergency, the less likely it is that the victim will get the help they need. The infamous rape and murder of Kitty Genovese in Queens, NY is often the go-to example to describe the phenomenon. Though it was later disproved that no one tried to help/ took notice in the incident, no one intervened to try and save her life despite her screaming. Similar experiments set up with graduates student confirmed the behavior time and time again. The explanation is that in a large crowd, each individual feels less personally responsible to offer aid. With the larger number of others who could do the same, others figure that their contribution isn't needed. Not everybody stood idle though. In test situations, individuals did intervene occasionally, but it was often when the person in need was a friend or somehow relatable to the person offering aid.
When one of the group members breaks the norm and either aids or defends the victim, then it is likely others will follow their lead. The article uses Flight 93 during the 9/11 crisis, who rose up and tried to overcome the bystander effect to stop the terrorist's mission. Overcoming the bystander effect isn't easy but someone needs to break the silence and it might as well be you.