A very smart post by Bill Gurley about the factors that contribute to the success of a marketplace.

A true marketplace needs natural pull on both the consumer and supplier side of the market. Aggregating suppliers is a necessary, but insufficient step on its own. You must also organically aggregate demand. With each step, it should get easier to acquire the incremental consumer AS WELL AS the incremental supplier. Highly liquid marketplaces naturally “tip” towards becoming a clearinghouse where neither the consumer nor the supplier would favor an alternative. That only happens if your momentum is increasing, and both consumers and suppliers are sensing an increasing importance of your place in the world. Much easier said than done.