Uber has some drivers in a city, and some passengers - not very valuable. But, Uber does something special, like drop prices, and all of a sudden, there a lot

Uber has some drivers in a city, and some passengers - not very valuable. But, Uber does something special, like drop prices, and all of a sudden, there a lot of people who hear about the low cost of UberX, and so they put the App on their iPhone/Android, and start calling vehicles. Drivers, hear about the incredible demand for UberX drivers, and start adding that network to their vehicle. Passengers discover there is always a Uber vehicle close by and so they start using it more often, which creates more demand. Eventually, you get a network of users/drivers - each new driver is available to many customers, and each customer will make themselves available to many drivers. It's not a perfect N(N-1)/2 mesh, but then neither were fax machines (not everyone wanted to fax everyone else) - but the same concept of network value exists.