The power of one vs groupthink

 Groupthink may be the biggest threat to our species in some ways, especially when it is augmented by the notion you mention, that, as "everybody knows," one person can't really do much. 

Rosa Parks was just one seamstress in one town in the South, but she sparked a movement that showed others what one person can do, offering a model that others emulated for a decade of nonviolent civil rights victories.

Greta Thunberg was just one Swedish girl in her teens, but she sparked a movement that sent thousands of schoolchildren out of school and into the streets in "Climate Strike Fridays," even resulting in insults from Trump when he was in the White House.

Julia Butterfly Hill was just one preacher's daughter from the South who climbed a Redwood tree that was slated to be cut down by a corporation taking down old growth Redwoods faster than ever. She stopped it, saved the tree, and launched a national movement to fight against logging the last of the old growth. 

A group of high school kids from Florida who had survived a mass shooting that killed 17 of their classmates refused to just be another group of young victims and they grew a movement in the US that drew millions into the streets to protest the easy availability of assault rifles. Now they are affecting dozens of races for seats in Congress to get gun control advocates in office.

Does standing up against the odds always work? No, and that's not the question. Can it work? Yes, and there are many more examples. When "everybody knows" feels wrong, it just might be.