I think most of the guys who go into the Marines and the SEALs and other parts of the service that're more selective and "gung ho" than others decide very early on in their lives that joining that particular branch or that particular unit is their ultimate goal. And to that end, they begin to adopt a mentality that'll enable them to not only survive, but thrive in that unit. This can start with simple things like doing their homework right or paying attention in class, and when they do that their grades, more often than not, skyrocket. But the bottom line is rock-stupid types don't last long in the military, at least not in any rating over, say, E-4. You do dumb shit and your peers will likely fuck you up for it.

I just don't understand the "dumb military guy" stereotype. Some of the smartest people I know spent some time in the service.