As someone who has been through basic training, I don't think of it as something that is done to someone. The recruit is still an active participant in it. I've seen many people wash out because they didn't realize that the military doesn't create that "whole-assing" spirit in you, but gives you the environment to create it in yourself. This bodes well for the idea that one can "do it alone".

However, I don't think you actually can. It's natural to reach periods where one can't find the motivation to go on and the temptation will be to give up. Unless you already have the dedication you're trying to create, it's very likely that you won't make it through those periods. This is where I don't think anyone can do this alone. People need someone to drag them through these periods. That's the function that basic training serves: it makes it very hard to give up.

In the end, I think it is possible to create that drive without joining the military. I don't think it's possible to do it alone. Hopefully, you can find someone to help, someone who will help push you through the low motivation periods and keep you going.