A 100% confidence rating isn't "common", but the applicant pools are so big the boards often pick candidates who have, among other things, 100% confidence ratings. That said, I know people have gotten selected with less than a 100% confidence rating, because the board is looking at the "whole person". The reasons for select/non-select are general ones, and each individual is different. Generally speaking, the board is looking for significant leadership experience (whether management, volunteer, sports, etc.), outstanding interviews and LORs, 100% confidence rating from IDCR OIC, civilian/military experience that is relevant to the community/ies to which the candidate is applying, etc. Still, there are so many candidates, it's possible for stellar candidates to be non-select.