On a literal level, Chris McCandless's biggest challenge was his final one: fronting the Alaskan wilderness alone, where he met unexpected hardships and had to cope with the inevitability of death at early age.
On a more profound level, McCandless's biggest challenges, as he well knew, were his own inner demons. He went to the Alaskan wilderness to challenge them, and from what we know from the writings he left behind, he won the inner battle even as he lost the outer fight for physical survival.
In journals he kept in the last weeks of his life, he recorded a change of consciousness. For example, after his failure with the moose he shot, he came to grips with himself and his disappointment and was able to write,
I am reborn. This is my dawn. Real life has just begun.
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