The first kid to stand up for someone being picked on often gives the whole room permission to follow.

Most people in a room already think something is wrong. What they are missing is proof that they are not alone in thinking it, which is why the first voice changes the arithmetic for everybody else. It is rarely the bravest person who speaks. It is the one who went slightly before the others were ready.

You do not have to make a speech to be first. Sitting down next to someone, saying that is enough, or leaving with them all count. If speaking up is not safe for you right now, telling an adult afterwards is also going first.