I think all cadets from all the academies cross this bridge at some point during there 4/C year. My daughter is at USAFA and she would say, though after recognition training, that everyone thinks about leaving and if they say they didn't they aren't being completely truthful. There is a difference though as to those who act on it. It is very much a "one day at a time mentality" through that first year. I am not sure if you can prepare for it, some days are just worse than others. The one piece of advice I came across last year that I passed on to my daughter was: If you decide you must leave, then you must leave on a good day when everything is going right. You must never make the decision to leave on a bad day, as it could be relative and you would not want to make a decision that could affect the rest of your life on just a bad day. Basically, I guess if they are all bad days, then you cross that bridge at the point where you can not take it anymore.
By the way DD is not athletically gifted and has sure had plenty of times when things weren't good, but she did stick it out and felt very accomplished after Recognition training in the Spring. Not sure if all Academies have the Recognition training or not, but it is like BCT all over again in the Spring for 3-4 days.