I believe it could often be like getting a certain MOS out of The Basic School for the Marines or a certain airframe out of flight school for any service. Often it isn't/wasn't your first choice, but you end up loving the community with which you live and work, you learn the mission (all have their pros/cons) and you eventually are proud of the job you do and enjoy the people you work with and are happy. There will be some who continue to covet the other job/airframe. Some of them will move given the opportunity. Some will make the right move, some will regret the move because it wasn't what they imagined.
Tough choices to make - but at least you are in the position to make them and that is more than many can wish for at the present time.