It's just like a normal person going out to train into becoming a soldier. Of course, when he comes back he won't be just as he left. He'd have known how to fight, how to kill and some other sorts they train them to do.
When you stay out in the woods for so long, there are some things that'll change, an example is the way you eat, the way you dress.
You'll just find yourself looking more like a cave man. Hehe.
I live the woods though but I don't want it to affect me too much.