I can't say for sure because I really don't know. I would guess that my persistence and preparation helped as well as my background. I did know a person at the unit I was selected at who wrote me a letter of recommendation and introduced me to a lot of people but in the end he said it was all me (I'm sure my knowing him didn't hurt). I've applied to every unit opening across the country from the beginning of June until now so to me it's a numbers game really. The more you apply the more opportunities you open yourself up to. Keep improving your scores if possible, building hours, improving your cover letter, getting better letters of recommendations and doing mock interviews until there is no topic they can bring up that you can't speak to.