Alone

"Only an animal does useful things," he said at last, after a long silence. "An animal gets food, finds a place to sleep, tries to keep comfortable. But I wanted to do something that was not useful - not like an animal at all, Something only a human being would do."

Gerard d'Aboville, Adventurer, author of Alone.

Go ahead, read the introduction by Paul Theroux. It's on the same website. I'm in the process of reading Fresh Air Fiend, and that's where I first read this narrative.