Telling a story about running late for his first computer science lecture and he threw on his shirt backwards AND inside-out. With the tag sticking out, he looked unkempt, and strange. No one would talk to him, except for one kid - KX Jin. "He just rolled with it." The two started working together, and now Jin is a big part of Facebook. Zuckerberg closed out the story with the most memorable one-liner "And that Class of 2017, is why you should be nice to people."
If the majority of people out there followed Zuckerberg's 13-word phrase, which many in the audience on May 25, 2017 waived it off as nothing or funny (it was pretty humorous), there would be a lot less school shootings.
Many educators were opposed to the Netflix series "13 Reasons Why" when it first came out. It deals with some hard-hitting issues teenagers face today. The reason is simple, teenagers are facing these issues is because people aren't listening to Zuckerberg's words. They aren't being nice to each other.
Something as simple as a playful joke through text message to one person, could be humiliating and hurtful to someone else. Not everybody's the same. Not everyone's feelings are the same. As the other person, you can't control how other people are going to feel. All you can control is how you make them feel, and they will remember that.
An example is shown in "13 Reasons Why" with Tyler Down. While what Tyler did was beyond stupid, and bordered on criminal, the other high schools students were also in the wrong for pushing him out. The other students included people Marcus Cole, who physically assaulted Hannah, as well as Courtney Crimsen, whose only goal was to save her own reputation by spreading rumors. It's no wonder at the end Tyler was shown with a trunk full of ammunition. Who could blame him? He had finally had enough. There comes a time where you will push people too far, through your actions (or lack thereof).
It's not about the guns. It's about taking responsibility, people looking themselves in the mirror, and asking what they could have done differently. Then, at that point start changing their behavior towards others. Zuckerberg is right, it's "why you should be nice people."