A number of comments seem to be wondering why YC doesn't provide detailed feedback to each rejected party. Some are assuming it's due to fear of discrimination claims, but I doubt that's the case. I would guess YC doesn't provide detailed feedback for three primary reasons:

1) They interview over 300 companies in a batch, and detailed feedback for each rejection would simply be time prohibitive.

2) They admit to being wrong occasionally, and will often fund companies on subsequent applications. Providing a laundry list of "things they dislike about you" would diminish that probability.

3) In most cases, it's probably less about your deficiencies, and more about the companies ahead of you. There may not be anything inherently wrong with the founders or company, you just got beat out by seemingly better alternatives (see point #2).

In any case, hustle on.