> It's not like a job, where if it sucks enough you can just leave and find a new one.

There's timing issues in some cases (and more issues during an emergency with stop-loss in effect) but otherwise if you are enlisted, you can not reup after your period of enlistment. If you are commissioned you can resign your commission. And you can almost certainly get another job, on favorable terms, because most public and many private employers apply hiring preference for veterans.