simplicity - he once picked up an attractive rock to use as a paperweight on his desk. When he later realised it needed dusting, and would thus uselessly occupy his time, he threw it out the window. He only worked as much as was necessary to supply his simple needs and spent the rest of the time doing more important stuff, like looking at trees.
I sometimes think about this while mowing my lawn (a job I hate) when I could be out in the woods. Can't remember the exact Thoreau quote, but he mentioned men who think they own their house, whereas really the house owns them.
An uncle of mine once told me that you "become a slave to your possessions." I dont know if he had read Thoreau but he was spot on the money with the philosophy. Will have to have to go and explore the world of literature myself. (now wheres my glasses).