I know it's a cliche' but it happens to be true. One day you wake up and you're just a few months shy of 40. You start thinking about decisions you could've made differently.
As a kid you were really into the military - you wanted to be a fighter pilot someday - but you got older and somehow you never got around to joining up. You ended up with glasses so you knew it was no use joining the air force. You know you would've drifted toward certain military specialties; the ones that took skill and brains, and since you're also kind of a door-kicker, they would've had to be dangerous. You'd be a Major by now and you'd be in Iraq doing something that mattered instead of shuffling electrons around on a computer screen or telling other people what to do.
Sometimes you still wonder if there's any way to get directly involved. You search the DOD website to see if there's anything that you'd be qualified to do. There isn't of course, but you still look, and who knows? You're a bright guy with some great language and tech skills. Maybe you'll even meet someone who knows someone who knows just the perfect place for you. Not too close to danger but close enough for you to feel like you're able to make a difference for someone else, for your country.
You make the mistake of thinking just a little too much sometimes. You begin to think about the implications of your decisions. You start to think about your comfortable life. The way you're always there for your kids birthdays, holidays, band concerts and other special events. You've never been gone for your wedding anniversary. No one worries that you won't come home from work. Their biggest fear is that your fast driving will get you hurt. You don't have war related injuries or back problems from bouncing through a humvee in the desert.
You only get one shot at this life. You make the best decision you can at the time and that's all anyone can do. You guess that you made the right decisions, but you still wonder.