Well, the brand is a byproduct of all the excellent work YC partners have been doing over the last 10 years. That being said, YC now has a strong positive selection advantage, the benefit of which is self-perpetuating.
No, YC is more than the brand. YC has an ethos, and the brand is a result.
The ethos is evangelism for basic business practices derived from common sense, rationality, and empathy.
The brand does have perks for founders, though. The network is actually that awesome, yes. YC is extraordinary for making it easy to raise a seed round. Some good ideas take time to mature, and a seed round helps them get momentum.
