The pools
Once you have been to FSP, and done the flying side of things you will sit your OSB. The OSB will determine whether or not you can be trained into a military officer (by you displaying the relevant qualities) and they will also take into account how well you did in the flying phase and the rest of the tests you complete during recruiting. If they feel that you can 1) be trained into a military officer and 2) be trained into a military pilot, you will receive a "recommendation" for further training.
Once you have that recommendation, you are then placed into the relevant waiting pool. There are many different pools because there are many different avenues of entry. The number and quality of people in each of these pools is constantly changing because new people join the pool and others drop out. Where you sit in those pools will also naturally change. What differentiates people is their score relative to each other, and that is based on all your scores throughout the entire recruiting process. When the ADF draws from the required pool, it will naturally take from the top. There are many people who miss out on a spot each year who have been recommended at FSP and gone into a pool.
To all those who read this post, I ask that you understand that the pools are CONSTANTLY changing and the needs of the ADF are also CONSTANTLY changing. I am not (read NOT) trying to put off anyone from applying - I fully encourage everyone to put in their best and give it a shot and I am happy to provide pointers when asked. I was in a very similiar position to Johnny Chase earlier this year and provided him with the info I had been made aware of.
Even at the worst times, those that are good enough to get through, will. It's as simple as that - do the tests, do them well, impress the socks off everybody and sit back and wait.