Well said. There's one thing I would add if you're doing defence work which is about security. The complications brought on by working with classified data can be very frustrating: limited or no internet access, limits on the software you can use, hassle presenting results at conferences etc, having to double check everything you write/say to the outside world to make sure you haven't said something you shouldn't. And no, knowing secret stuff isn't worth the hassle - most of it isn't even interesting anyway.