In walden, why did henry david thoreau leave the woods to return to civilization?

In Walden, Thoreau details his experiences of living in a cabin he built near Walden Pond, which was owned by Ralph Waldo Emerson. This was an attempt to engage in a social experiment, and return to a simple life of self-reliance. Thoreau lived in this cabin for two years, two months and two days. However, after this time, he started feeling that his time there had been enough. He claims that he started falling into an easy routine, and that it was necessary for him to pull himself out of it, as he had several lives to live and could not spare any more time on that particular one.

as much wood as a woodchuck could chuck if a woodchuck could chuck wood.

sadly it cannot chuck wood

adverb is the answer i believe.