We all know the drill: As soon as we hear of a sexual assault, we focus on what the victim could have done to prevent it. This past summer, a woman who is blind was sexually assaulted while walking with her guide dog near the State House. Most news reports correctly noted that people with disabilities are twice as likely to be assaulted as the general population. They also focused on how unusual it was for someone accompanied by a dog to be assaulted and lamented that there really wasn’t anything the victim could have done to protect herself.

But these are the wrong things to be focusing on. We will never end the epidemic of sexual assault until our first instinct is to ask why someone would commit such an assault in the first place and our second is to ask why most people who witness these events fail to intervene.

Thanks to Donald Trump, nearly everyone is now familiar with the term “bystander” as it relates to sexual assault. In one of the many explosive newsmaking incidents of the presidential campaign, video was made public of Trump describing to then-Access Hollywood anchor Billy Bush how he gets away with assaulting women because he is famous. Bush can be heard giggling at Trump’s stories and exclaiming that Trump can do “whatever you want!”

Few bystanders behave as Bush did. More typical behavior for a bystander is to simply turn away when they see harassment or assault. A 2013 survey of Boston-area residents found that 476 out of 543 respondents, or 88 percent, had experienced sexual harassment or assault. Just 14 percent said a witness had intervened on their behalf.

Bystanders can feel scared or simply not know what to do. Given that one of the most effective deterrents to sexual assault is bystander intervention, efforts to educate the public on how to safely intervene are key to lowering rates of sexual assault.

In early November, the MBTA launched a public awareness campaign aimed at T riders encouraging them to report incidents of sexual harassment. For three months, 800 posters will be on display on trains, buses, and in T stations. The posters explicitly depict people with disabilities, shown as both survivors and as bystanders successfully intervening.

The new posters are the latest in a series of anti-sexual assault campaigns the T has run in collaboration with the Boston Area Rape Crisis Center since 2008. We know that they are making a difference: After the first campaign, reports of assault and harassment to Transit Police increased by 32 percent, and arrests for indecent assault and battery increased by 40 percent.

The advice given to witnesses on the T applies to all public spaces. Bystanders can call 911. They can record a video or take a photo and send it to law enforcement. They can make eye contact with the person being targeted and ask if they need help. They can create a distraction by pointing out what’s happening to other people, asking for directions, or starting a conversation. Bystanders can also call BARCC’s hotline for support: 800-841-8371.

 This can take courage. But what bystanders should never do, under any circumstances, is follow Bush’s lead and play along.

Gina Scaramella is the executive director of the Boston Area Rape Crisis Center.