I am alarmed when it happens that I have walked a mile into the woods bodily, without getting there in spirit. In my afternoon walk I would fain forget all my morning occupations and my obligations to society. But it sometimes happens that I cannot easily shake off the village. The thoughts of some work will run in my head and I am not where my body is - I am out of my senses. In my walks I would fain return to my senses. What business have I in the woods, if I am thinking of something out of the woods? I suspect myself, and cannot help shudder, when I find myself so implicated even in what are called good works - for this may sometimes happen.

Henry David Thoreau, Walking