YC is one potential path to success, and they have their criteria, which OP's idea and current business did not meet. That doesn't mean the idea won't be successful. Just keep at it, OP. Don't let rejection from any one investor have an out-sized impact on your attitude. If you believe in the idea just put your head back down and get back to work. Look at it this way: the further along you are when you take on investors, the more you keep.