What is the best way to lead a new soldier who is uncertain if they even want to be in the army?

It takes time away from good soldiers who want to be there. Been there. Kick them out and move on. It's not a discipline problem, it's a lack of responsible upbringing, and it's not worth wasting time on. You don't want to be here, simple gtf out.

The new soldier is uncertain as to whether he, and who else, wants to be in the Army?

I have told soldiers that if this is your first duty station and you are unsure if you want to stay in or not....at least reup and change duty stations or reclass. Many soldiers base their experience off of their present duty station. They have nothing else to go off of. If they are having a tough time dealing one can see how it is easy to just give up and get out at ets. We all been there... If he or she stay the course they will not regret it. I have also asked soldiers whether or not they are staying in and I get from time to time,"I don't know". And I usually respond with,"Well that is a good answer because there are so many doors to choose form with "I don't know". the sky is the limit..or at least as high as the in and out calls go....lol

You need to find out the source of their feelings for why they want out. Then address the issues as the soldier presents itself. I wish I had nco's that cared enough about the issues of their subordinates to get to the source of the issues at hand. It very well could of changed my attitude twards wanting to stay in. Now I'm not saying that subordinates need to be babysat. Let's face it some actually need that an you don't get paid enough for that. However having an nco actually care about his soldiers could make the difference.

Nobody nowadays is drafted -- every member of the military is there because he joined of his own free will and accord. He had ample time to consider his options before he joined. He made his choice, so he should live with it.
The only valid reason to join the military is to serve one's country. All else (schools, particular assignments, etc.) is secondary.
If someone joins the military, then whines "I don't wanna play soldier no more," explain to him that he made his bed and he can lie in it. If he still refuses to get with the program, give him undesirable duty, such as permanent latrine orderly. If he goes UA/AWOL, have him face a court martial -- reduce him to E-1, forfeiture of all pay and allowances, confinement at hard labor for (at a minimum) the duration of his enlistment, and a dishonorable discharge -- and make the news of that sentence public.

The best way would be to educate him the more in order to make him understand even better

I can't speak to the Army but it's the same issue regardless of which service. You have a member of the unit that is debating their future in the military and since people are the most valuable asset you have, you have to fix it. Use positive leadership with all members in the unit. Take the time to find out what the problem is and give it your best shot to fix it. Develop an action plan with realistic goals and get them to buy into the plan. If the member feels ownership in the plan they may begin to see that they control their destiny. They will be more likely to respond to a plan that they agreed to than one you are imposing on them without their input. The loss of motivation may be the result of failed or marginal leadership or a legitimate problem that nobody was aware of and whether you like it or not it's happening on your watch and it's worth the effort to salvage them. Remember that this is someone's child and in a perfect world we wouldn't face these challenges, but the military is far from perfect. It makes more sense to try and turn them around than kick them to the curb. Leaders often spend 90% of their time on 10% of their unit but it comes with the territory. You won't save all of them but that's reality, so once you see it's a lost cause then let the Chain of Command do their job by cutting them loose.

You explain to them their commitment and requirements! You work with them to teach their potential while reminding them of the consequences of their potentially negative actions!

We all know what we are signing up for. There's not been a draft since Vietnam. I say push them just like you would push any other recruit. The military has changed a lot since I served. We have to push recruits in order to break them down and then build them back up. A person, especially someone who's seen combat knows that you can't be weak and do your job. Your responsible not only for yourself, but for your brothers and sister on that battlefield with you. It's not a game. If your weak, physically or mentally, then someone dies. If a recruit goes through boot and comes out the other end, they will never again know such pride.

Every person is different, and joined for different circumstances. I joined because it was in the wake of 9/11, and it was the feeling of patriotism I had at the time. When the few guys I supervised and brought up displayed "uncertainty" it was a case by case basis. I always reminded them they signed up to do great things, and the benefits of their service, and sacrifices would either urge them to stay in and continue until retirement, or to finish their contracts and proceed to whatever they had planned. Reminding them that actions like, the ones I believe we're trying to address gets them nowhere, and is harmful to the life they'll be living after their discharge. I always emphasized the more they rebel, or step out of line, the more, and more the enlistment becomes like a prison sentence. We all signed up for our own reasons, but while we're fulfilling that service, we're all hear to do a job.