We're far enough along, and we have enough buzz among companies testing our app already, that we're not worried at all. YC wasn't a make-or-break deal for us by any means. Good to hear it's not for you too. If you really believe in your idea, it shouldn't be for anyone on here.
I think my idea is great.
It's more of a "can I do anything to improve". I believe in always trying to find ways to be better. If my idea was rejected because they thought it was too niche, I would want to know. If it's because I couldn't think of other things I've done, I'd like to know. etc, etc.
I agree that a positive, confident attitude is probably productive, but you made your point by turning the positivity against Y Combinator because you are upset that you were not accepted. Right?
As for my success, I built a shareware business that made me significantly more than my salary, as a single founder, while still working full time. It enabled me to leave my job and work for myself.