Whether a Soldier, Sailor, Marine, or Airman, people choose to serve their nation's military, and the U.S. refers to them all as Military Service Members.
Why we serve is for a variety of different reasons.
Some do it out of familial tradition. Some as the only option to follow for college after high school. Some choose it instead of going to jail. And many choose because of the lack of jobs in their home communities.
Whatever the reason, it is understood that to serve is to put your life on the line. To sacrifice your life to the defense of the state, should the need arise. Once the reasoning is understood, you can then pursue any service branch, and any job that suits you or interests you.
For me, there were a couple of reasons why I joined.
Having just graduated college and finding no job prospects back home, it literally became my last viable option other then hunting for something which was not there in my home area.
No one in my immediate family, or even to the extent of my parent's cousins, were in the military at the time, and other then having an uncle who was in the Air Force since the end of WWII thru Korea and Vietnam, only my grandfather's generation had people who served during WWII.
Having read about kamikaze pilots for Japan during WWII, many of them were college educated, and remarked in letters home how they knew what they were doing was foolish and not likely to achieve anything great, but saw their actions as a life debt they were giving to the state, and the Emperor, for the lives they were able to lead up to that point.
For me, to serve was a way for my family to exchange a life debt of peace and relative prosperity since around fifty-five years the U.S. govt had never drafted any of my family members for military service.
The thing is, after a while of enlisting, my personal reasoning for joining changed in my mind. A sense of patriotism, and of defending the nation, became part of my thinking and reasoning. (I later realized this was the "thought control" the military exerted on us, which can be difficult to resist since it is subtle and everywhere.)
Serving is more then agreeing to a tough life and a lot of training. There are chances to go to school, to learn and expand, to enjoy your own personal pursuits and desires, to fully enjoy your own personality and interests. Course, this all depends on where you are stationed, and the "shop" you work in.
Training, though, is the most amazing thing anyone can participate in.
To witness average, sometimes weak, individuals become physically and mentally strong is an awe-inspiring experience. Especially when it happens to you.
So, the personal story of everyone who serves is both the same and wildly different. The understanding, though, is the same. You are made into a stronger person, a living weapon even.
When I went thru the Army basic training, my comrades and I were amazed at how such a short period of time felt longer. And when we watched films like "Full Metal Jacket," remarked at how we wished our training was more like that we saw portrayed (the physical exercise, not the mental issues the DI caused).
The actual feeling of being a Soldier, the sense that what I felt within was the new me, did not occur till months after joining. And even then, that was skewed since I spent around a year and a half lost in the training side of the Army.
To be in the U.S. Army for a year, and still considered a raw recruit, and treated as such by a pompous Drill Sergeant, likely hurt my view of how the large entity that is the U.S. Army was not all filled with stellar leaders and people who wanted to be part of an amazing group. But that is what you get for a "mechanism" like the U.S. Army Training Command.
It did not help to keep motivation up, though.
But, luckily, I had discovered my own reserves of self discipline and strength prior to joining the military, and used those to help me endure the mental stresses which came from being forced to live in cramped quarters next to ungrateful recruits and having to endure almost childish games put on by leaders.
Everything is a learning experience.