That it happens suddenly somewhere very unecpected. And that they are all doing the same.
surprise. That i is not expected at all and that "it" put up a great show.
In rare cases, precise coordination and out-of-the-box creativity
Many people, in a place with loads of observers and a fun concept
One that inspires people to think differently and take an active part in solving the pressing social and environmental issues which the human race is currently facing.
Coordination
when a lot of people sees it, when people like it and engage in it, when you surprise them in a good way, when there is a lot of media coverage of it afterwards