Peter Rip has a nice comment:
Early stage companies go through predictable phases. First, it is about the Product. Then it is about the early Customers. Then it is about the Partners. Then it is about the Investment Community. All along the team is changing, expanding, and improving.
The successful early stage companies have two fates they either get acquired at nice prices or they go public. Either way, these companies benefit enormously from having friends that run in those circles.