In The Tipping Point, Malcolm Gladwell wrote about how an bar fight might grow. Everybody has their own “tipping point” for how many people have to be fighting to engage themselves in the fight.
Something similar is seen in this video, from the Sasquatch Music Festival 2009, where this one guy just needs to dance. Two more guys come up to him, seemingly making fun of his dance moves. But then something happens (around 1.10 into the movie). More and more people join in, and all of a sudden, everybody has reached their tipping points of how many other people it takes on the “dance floor” to make them start dancing.
Take a look for yourself! This is how movements start, how ideas and phenomena spread in society, and how culture eventually changes. The more people in your surroundings that are acting in a specific way, the more legitimate it becomes to act the same. And before you know it, societal norms have changed.
Via Brains on Fire.