...most clearly in communication media. Say you wanted to talk to 10,000 people once a day. Unless you wanted to speak to a group bounded by geography--a small town, or a subset of a small city--you'd be stymied. You can broadcast to a million unknowns hoping you happen to catch some of the 10,000 you want, or you can slowly collect the names of individuals who contact you, one by one, and transmit to them directly. Neither way is elegant. Retailers call this the "hard middle," because it is so hard to service a group of 10,000 customers who share a common interest but not a common geography. Retailers crave the middle because they have learned that you can't appeal to folks with a simple naked exchange of money. You need other essentials of marketplaces--conversations, loitering, flirting, people-watching. Before you can have commerce, you need a community, a middle number of interacting people.