Can a Servicemember truly "manage their career"?

Absolutely. As long as you're proactive and you make reasonable requests, you can certainly manage your career quite successfully. I always indicated to my superiors and to my assignment officers where I wanted to be stationed and the types of jobs I wanted to pursue, and I was always successful at getting the assignments that I wanted. I was also able to attend the schools I wanted, both military and civilian. No complaints here at all. The only time I came close to not getting what I wanted, I was able to manage my way out of it. Someone who is currently a MG (was a MAJ at the time) wanted to assign me to Fort Hood for company command. I was able to get company command in the 101st (which was what I wanted). It just took some proactive work on my part.

You can manage what you do. Get the required schools as soon as you can, go beyond required schools if possible. Take those crummy assignments no one else wants ...

I'm actively trying to prove this concept! In the civilian sector, we preach of the power of networking, mentorship, and of community; this allows some to outmaneuver their peers, bypassing and climbing faster than the average bear. That level of meritocracy and active career management is, of course, not how our military works. Sure, there are BZ boards, but most people come up together, learn together, and promote together. Those who are able to pull out ahead seem to play a better long game than others; as BG Earhart called out on your other post, there are plenty of people who top out at MSG or COL. While those are surely respectable ranks and careers, the ones who truly manage their careers well seem to be able to navigate to the highest and most visible posts.

Help me prove that you can manage your career by chiming in on my current struggle: S2 be or not S2 be?

https://www.rallypoint.com/answers/are-there-any-downsides-to-being-a-battalion-s2-any-reason-it-may-negatively-impact-promotion-boards-in-the-future-any-negative-sentiments