Edit: Looks like my last post didn't manifest and I just now noticed.
I didn't start playing D&D in order to learn anything. I play to relax, to socialize, to have fun. I play because it's interesting, it's exciting, it's diversionary. Not to learn a lesson.
But, of course, you learn something from any activity you participate in. Role playing games can teach a number of different lessons. The single most important lesson I've learned from playing D&D? Flexibility.
As a player, you have to flexible when facing the challenges presented to you during play. The obvious answer may not be the one that works. As a DM, you have to be flexible when your players perform some completely off the wall action instead of what you expected them to. In order to set up a session you have to be flexible in order to accommodate everyone's schedule as best you can. And a certain amount of flexibility is useful in bringing the disparate personalities around the table together into a functional gaming group.