You are learning to work with a group, be part of a team, support those around you, and not because you're told to, but for the sole reason that it just feels right. The respect you earn and give are 100% developed on action, which can't be said for other places in life.
You work on weaknesses, learn how to fail, and how to communicate those failures into a plan to keep attacking those goals. This in itself is something I have yet to find a group of people successfully accomplish. A majority of people these days stand down at the first sign of difficulty, but not here. It is a place of possibility and looking for solutions rather than problems.