Basically feedback falls into 2 broad categories: "you are YC material but we have 2000 applicants like you and only 100 slots" or "you are not YC material because you don't solve a problem/have no experience/no market/no traction".
In either case if you are serious about your startup, the next steps should be the same: keep hustling to make your startup better, try new things, fail, learn from your failures and try again. And keep applying.
I suspect that even if you are not "YC material", the fact that you kept hustling and survived a dozen rejections is proof that you are.
