What is the main idea of Into the Wild?

Chris McCandless, aka Alexander Supertramp, experiences
various enlightening moments that unfold the main idea in the novel, "Into the Wild". 
Jon Krakauer clearly portrays this main idea of his novel:  a young man attempts to find
true happiness through solitude and nature, instead of finding it in society. 
Throughout the text, Chris interacts with characters that differ in lifestyle,
particular views about life and society, age, gender, and motives.  The more Chris
travels, the more his ambition to enter the "wild" is validated.  He has several
contemplations that challenge his departure, but the amount of sadness and dysfunction
among humans only pushes him further away from society.  The ending events challenge his
aspiration to be alone in nature as he is challenged psychologically and
physically.