It's hard to appreciate unless you've been on the other side of rush how totally RANDOM a cut can be. Someone in a house can be pulling for you but maybe they don't have a lot of clout in the chapter. Your name can come up at a time when everyone is exhausted and just wants to go to sleep so nobody fights for you unless they're incredibly passionate. You might get mixed up with another rushee. Sometimes people are petty beyond credibility. Maybe you dated their sister's ex-boyfriend or you got homecoming court instead of a sister's cousin's friend. Or maybe you took her pencil in third grade. Lack of sleep, stress and tension, all these things can bring out the worst in us.
DIRTY LITTLE SECRET: Another thing that the mom's of PNM's need to be aware of is that sometimes you may think you have a rec to a house that never got sent in.
I have seen this happen. The alum just never got around to it or misplaced it or didn't know what to say. ALWAYS get two recs. And a personal letter if you can. (That's for competitive rush. Smaller schools or non-SEC schools may look on that as overkill.)