Serving in the army (and actually going to war, which is a nightmare, for a brief period):

1. It helps you get discipline right, and care less about "productivity" and "motivation" - you just do stuff. 2. It teaches you that your reserves and powers are limited, and priorities are an hourly grind of making the right choices. 3. It teaches you to stay sharp all the time, no matter what your body tells you to feel.

Not that I've mastered any of these, but even small hints I've picked up really changed my life before/after spending 6 months in pre-field training and a year in field (I was officer-in-reserve before, but it teaches you knowledge, not skill).