In the spring of 1845, Thoreau moved to a small house he had built himself on the shore of Walden Pond, with no particular plan beyond finding out what an ordinary day actually required. He explains the experiment plainly in the chapter called "Where I Lived, and What I Lived For":
I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived.
What follows that line is not a monk's renunciation but something closer to an audit. He wanted to know which parts of a life were structural and which were decoration mistaken for structure — furniture bought to fill a room rather than to live in it. His answer, stated a few pages later, is almost a chant: "Simplicity, simplicity, simplicity! I say, let your affairs be as two or three, and not a hundred or a thousand." The claim is not that fewer possessions make a person virtuous. It is that a crowded life leaves no clear view of anything in it — the days blur together under an accumulation nobody quite remembers choosing.
Seneca had recommended almost this exact exercise two thousand years earlier, though as a thought experiment rather than a two-year lease. In his seventeenth letter to Lucilius, he urges his friend to set aside a certain number of days, eating the plainest food, wearing the roughest clothing, and asking the whole while: is this truly the condition I have been dreading? Seneca's point in prescribing the rehearsal was that most people fear a scarcity they have never actually tested, and so they keep working past the point of any real need, just to stay safely clear of a poverty that may not even feel like poverty once tried. Thoreau, without necessarily meaning to, ran that rehearsal all the way through. He did not report back with complaints. He reported that beans, a hoe, a pond to swim in, and long unscheduled hours turned out to contain most of what a person actually wants from a day — and that the rest had been noise mistaken for necessity.
Neither man is arguing that comfort is bad or that hardship is secretly good. The argument is narrower and more useful than that: that nobody can tell which of their current expenses are load-bearing until something is actually removed and the structure is checked for damage. Most of it, it turns out, was never holding anything up.
A short version of the same test needs no pond and no cabin — just one ordinary Saturday, spent without buying anything, checking anything, or improving anything, to see how much of the day was still there once the errands were.