Possible? Yes, I think so. It would just take an incredible inner strength to keep at something when the results aren't necessarily tangible or immediately recognizable to you. I'm sure that if you went off into the mountains or something and taught yourself how to be disciplined, then people would notice. You may have a hard time, because you underwent the transformation and therefore the effects of the change were gradual for you.
The Army works because you have a team that is all about accomplishing the same task. Run over here, go pick up these rocks, everyone dig a hole, etc. You get instant positive or negative reinforcement based on your performance. Sometimes, they use negative reinforcement anyway because they want a soldier that is going to obey an order, even if it sucks. The recruits also have the drill instructors there to keep them on task, to push them and motivate them when things are rough. As a person who would be going for it alone, you have to be completely self-motivated to accomplish your goal.
I don't have a definite solution for you, but perhaps writing down your goal and any progress you made towards it would serve as a reminder of your accomplishments and possibly motivate you when things seem to be overwhelming.