Both of these men were escaping society and the reality of everyday life. The aspects of everyday life were different when Ruess was alive, when McCandless was alive, and even now. Today you could be escaping your family, friends, or peers. You could be escaping the technology of today and how it controls some people lives. Taking time to forget about these things and leave all of your responsibilities behind is important for your mental and emotional health.
I however would not be able to escape these realities for the length of time that these former adventurers did. I could escape them for a few hours, days, or maybe even weeks, but not for months and years at a time. I would miss spending time with my family and friends. I think the solitude and loneliness would drive me crazy. I would also miss being able to have instant contact with people anytime I wanted. This goes hand in hand with the relationships I have that I would be leaving.
Although Ruess and McCandless survived like this, it is not a life everyone can endure. You need to be street smart and know things about the natural world. It is a very bold lifestyle for anyone, but people that live the way McCandless did often thrive in that environment in a different way than they did, or seemed to in the modern environment. They changed their reality into something they wanted, which is a truly admirable feat.