As an entrepreneur, you're going to get rejected over and over again. Why should that change how you approach potential future rejections? As investors, YCombinator wants to see that you won't give up in the face of setbacks...you are now giving up in the face of setbacks. The value of a YCombinator investment does not change depending on whether they have chosen you or not. Why has your decision whether to pursue it changed?
(Full disclosure: I've been rejected 4 times from YCombinator. Also rejected from FriendFeed, LikeALittle, Twitter, and Harvard. Stupidly passed up DropBox. Accepted by Amherst and Google. My opinion of any of them has not changed based on whether or not they rejected me. I haven't applied to YC since SFP08, but that's because my interests at present lie more in technology than in startups, and other opportunities have been available to me in that area. That does not mean I would not apply to YC again should I have a burning desire to start a company.)