Common characteristics: self service customer acquisition, critical mass, runaway user growth, winner take all markets, complex ux, network effects, typically create new ways for people to interact.

The more people use them, the better they work, and more people use them all the time—a kind of self-stoking mass collaboration that wouldn't have been possible without the Internet.

Were it not for these counterbalances, humankind would self-destruct out of the sheer mass of its unopposed negativity.