Persistence & determination are two of the most important factors. Why hang your dreams on any particular group? I say know what you want to do and let nothing stand in your way. And for Y Combinator? They simply can't support the dreams of everyone that applies. Not everyone is going to fit with what they are comfortable with and wish to get behind to support. If you get to the interview stage as this group did and are rejected, obviously the feedback can be fuel and added direction to further shape your vision going forward.