It is definitely natural. The academy even expects it. Minus the economy being a factor in a higher retention, it is not uncommon in the past for 50+ to simply quit during basic training. It simply wasn't what they thought it would be. And unfortunately, until you're there, you have no true idea of what you're getting into. And we're talking about people who said "I've wanted to go to the air force academy my WHOLE LIFE". In the past, there would be on average 1200-1300 appointments per year, and within 4 years, the graduating class would be approximately 950-1000. Some were dismissed for academic, honor, and other administrative reasons; but many simply quit within their first 2 years. It simply wasn't what they though it would be.
And even the most knowledgeable cadets, who know the most about the academy, such as military brats; even many of them don't realize exactly what they were getting into. So when you ask; what were they expecting that they didn't find, and then want to leave the academy....... I don't think it's so much a matter of WHAT, but rather HOW! When I say HOW, I mean that most people coming to the academy don't realize how much time and effort is going to be required of them. I don't think they realize how they are going to be treated in order to reach the air force's goals for their training. I don't think they realize how little control they have over their own lives and decisions. The air force is a way of life. It's something that much bigger than any one individual. And the academy is just the beginning of that way of life. Yes, once you graduate and get commissioned, you'll have a lot more freedom and say so over your future. But it's not absolute. Everything from your dress and appearance to your conduct on AND OFF duty is dictated. I think that's the part that most people who quit the academy come to realize, and decide they can't live that way.
Unfortunately, many believe that if they go off to ROTC or graduate college and get commissioned through OTS, that somehow it's going to be different or better. It isn't. The air force (military) is still the same. And this isn't just an academy cadet thing. There are many enlisted who think the military is something they've always wanted too. Then, they realize it's not what they thought it was going to be. They do their 4 years and they get out. So I don't think that there's really any expectations that the cadet didn't find; but rather I think they just didn't realize how much work and sacrifice it takes to achieve those expectations of a quality education; serving your country; and being part of something bigger than yourself, where the "Needs of the Many, outweigh the needs of the Few".