I have a friend who was waitlisted in middle tier at certain a medical school and another unranked waitlist last year . . . he has a 3.8 GPA and 30 MCAT student, tons of EC's, wants to practice in the same state as the school, and good LOR's. He ended up not being accepted. This year he applied earlier, got another year of EC's working as a tech in the ER, additional good LOR's (from Physicians he worked with), and he applied to a lot more schools (including more lower tier schools). So this year he is rejected post interview at the school he was in the middle tier at last year, not interviewed at the other school he was waitlisted at and he is now sitting on 4 other waitlists (still no acceptances). You might argue he did not interview well, but since I have known him for 8 years I find that hard to believe (especially for having 6 interviews . . . you would think one would pay off). I think he was just unlucky.
edit: there is also luck in where you live (it is much harder to get into medical school from a western state), who you interview with (different interviewers look for different things), and a myriad of other factors. Given enough time an applicant can move to another state, attain residency, interview enough times to get the right interviewer etc . . . but for first attempt applicants there is a lot of luck involved.