Thoreau is inspired to embark on his quest for spiritual enlightenment by his own desire to find out what life really is all about. He's dissatisfied with contemporary society and questions whether modernization has really improved the quality of life. He's basically called to question the world around him.
Thoreau decides to live alone at Walden Pond and he lays out his rationale: it is a private experiment to see whether it is possible to live a rich and fulfilling life without all the luxuries of modern life.
When Thoreau arrives at Walden Pond and begins to set up his home, he doesn't experience much frustration. Everything generally goes according to plan, with a few minor hiccups like a neighbor stealing his nails. So, arrival? Yes. Frustration? Not so much.
Over two years, Thoreau enjoys life at the pond as it changes over the four seasons. He experiences what many might consider to be hardships: he lives on a diet mostly of tasteless bread, he gets snowed in during the winter, he is often alone, and he spends much of his day laboring in his garden. For Thoreau, though, these hardships are welcome opportunities for learning. If only we could all see the world that way.
Satisfied that he has learned all he can from his two years at Walden Pond, Thoreau sets out to join civilized society once again, enriched by his experiences.