For that, I think I'd look to Norman Maclean's _Young Men and Fire_ where he talks about smoke jumpers:
"It is very important to a lot of people to make unmistakably clear to themselves and to the universe that they love the universe but are not intimidated by it and will not be shaken by it, no matter what it has in store. Moreover, they demand something from themselves early in life that can be taken ever after as a demonstration of this abiding feeling...
"For many former Smokejumpers, then, smokejumping is not closely tied up with their [eventual] way of life, but is more something that is necessary for them to pass through and not around and, once it is unmistakably done, does not have to be done again. The 'it' is within, and is the need to settle some things with the universe and ourselves before taking on the 'business of the world,' which isn't all that special or hard but takes time. This 'it' is the something special within that demands we do something special, and 'it' could be within a lot of us."
If people here are reading this and haven't already realized some parallels between not just McCandless and smokejumpers but also entrepreneurs I'd be surprised.
Now, you can draw distinctions between McCandless and smokejumpers, too: the later train and drill and prepare, probably as well as Amundsen could be satisfied with. And their work has a practical end. But their work is still an adventure because they also operate in an area of high risk, and as a result they sometimes pay a high cost.
And they don't do this job for entirely practical reasons. They do it because they have a need for an internal narrative that settles certain things and establishes a kind of identity, they do it because they need something off the beaten track for middle class success.
McCandless was clearly looking for that. I think it's fair to ask if he'd been a little less romantic about it and a little more thoughtful whether he might have had both his survival adventure and his survival.
Then again, unless you're Batman or some other protagonist whose superpower is acute anticipation by authorial fiat, it's mitigated by the limits of the best laid plans.